Fair Value Measurements - Fair Value Measurements by Level for Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Sep. 30, 2024	Dec. 31, 2023
Assets
Cash and cash equivalents	$ 14,577	$ 17,193
Investments:
Equity securities	15	17
Total assets at fair value	35,603	36,317
Total liabilities at fair value		13
Accounts payable and accrued expenses: \| Currency Swap
Investments:
Derivative liability		13
U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	594	395
Corporate securities
Investments:
Fair value	10,689	9,601
Municipal securities
Investments:
Fair value	4,142	3,985
Short-term time deposits
Investments:
Fair value	875	746
Asset-backed securities
Investments:
Fair value	1,778	1,638
Residential mortgage-backed securities
Investments:
Fair value	1,668	1,407
Commercial mortgage-backed securities
Investments:
Fair value	1,189	1,072
Level I
Assets
Cash and cash equivalents	14,577	17,193
Investments:
Total assets at fair value	15,258	17,862
Total liabilities at fair value		0
Level I \| Accounts payable and accrued expenses: \| Currency Swap
Investments:
Derivative liability		0
Level II
Assets
Cash and cash equivalents	0	0
Investments:
Total assets at fair value	20,345	18,455
Total liabilities at fair value		13
Level II \| Accounts payable and accrued expenses: \| Currency Swap
Investments:
Derivative liability		13
Level III
Assets
Cash and cash equivalents	0	0
Investments:
Total assets at fair value	0	0
Total liabilities at fair value		0
Level III \| Accounts payable and accrued expenses: \| Currency Swap
Investments:
Derivative liability		0
Investments
Investments:
Fair value	19,559	17,721
Total investments	19,574	17,738
Investments \| U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	56	62
Investments \| Corporate securities
Investments:
Fair value	10,649	9,564
Investments \| Municipal securities
Investments:
Fair value	3,344	3,232
Investments \| Short-term time deposits
Investments:
Fair value	875	746
Investments \| Asset-backed securities
Investments:
Fair value	1,778	1,638
Investments \| Residential mortgage-backed securities
Investments:
Fair value	1,668	1,407
Investments \| Commercial mortgage-backed securities
Investments:
Fair value	1,189	1,072
Investments \| Equity securities
Investments:
Equity securities	15	17
Investments \| Level I
Investments:
Total investments	70	77
Investments \| Level I \| U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	56	62
Investments \| Level I \| Corporate securities
Investments:
Fair value	0	0
Investments \| Level I \| Municipal securities
Investments:
Fair value	0	0
Investments \| Level I \| Short-term time deposits
Investments:
Fair value	0	0
Investments \| Level I \| Asset-backed securities
Investments:
Fair value	0	0
Investments \| Level I \| Residential mortgage-backed securities
Investments:
Fair value	0	0
Investments \| Level I \| Commercial mortgage-backed securities
Investments:
Fair value	0	0
Investments \| Level I \| Equity securities
Investments:
Equity securities	14	15
Investments \| Level II
Investments:
Total investments	19,504	17,661
Investments \| Level II \| U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	0	0
Investments \| Level II \| Corporate securities
Investments:
Fair value	10,649	9,564
Investments \| Level II \| Municipal securities
Investments:
Fair value	3,344	3,232
Investments \| Level II \| Short-term time deposits
Investments:
Fair value	875	746
Investments \| Level II \| Asset-backed securities
Investments:
Fair value	1,778	1,638
Investments \| Level II \| Residential mortgage-backed securities
Investments:
Fair value	1,668	1,407
Investments \| Level II \| Commercial mortgage-backed securities
Investments:
Fair value	1,189	1,072
Investments \| Level II \| Equity securities
Investments:
Equity securities	1	2
Investments \| Level III
Investments:
Total investments	0	0
Investments \| Level III \| U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	0	0
Investments \| Level III \| Corporate securities
Investments:
Fair value	0	0
Investments \| Level III \| Municipal securities
Investments:
Fair value	0	0
Investments \| Level III \| Short-term time deposits
Investments:
Fair value	0	0
Investments \| Level III \| Asset-backed securities
Investments:
Fair value	0	0
Investments \| Level III \| Residential mortgage-backed securities
Investments:
Fair value	0	0
Investments \| Level III \| Commercial mortgage-backed securities
Investments:
Fair value	0	0
Investments \| Level III \| Equity securities
Investments:
Equity securities	0	0
Restricted Deposits
Investments:
Fair value	1,452	1,386
Restricted Deposits \| U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	538	333
Restricted Deposits \| Corporate securities
Investments:
Fair value	40	37
Restricted Deposits \| Municipal securities
Investments:
Fair value	798	753
Restricted Deposits \| Cash and cash equivalents
Investments:
Fair value	73	259
Restricted Deposits \| Certificates of deposit
Investments:
Fair value	3	4
Restricted Deposits \| Level I
Investments:
Fair value	611	592
Restricted Deposits \| Level I \| U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	538	333
Restricted Deposits \| Level I \| Corporate securities
Investments:
Fair value	0	0
Restricted Deposits \| Level I \| Municipal securities
Investments:
Fair value	0	0
Restricted Deposits \| Level I \| Cash and cash equivalents
Investments:
Fair value	73	259
Restricted Deposits \| Level I \| Certificates of deposit
Investments:
Fair value	0	0
Restricted Deposits \| Level II
Investments:
Fair value	841	794
Restricted Deposits \| Level II \| U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	0	0
Restricted Deposits \| Level II \| Corporate securities
Investments:
Fair value	40	37
Restricted Deposits \| Level II \| Municipal securities
Investments:
Fair value	798	753
Restricted Deposits \| Level II \| Cash and cash equivalents
Investments:
Fair value	0	0
Restricted Deposits \| Level II \| Certificates of deposit
Investments:
Fair value	3	4
Restricted Deposits \| Level III
Investments:
Fair value	0	0
Restricted Deposits \| Level III \| U.S. Treasury securities and obligations of U.S. government corporations and agencies
Investments:
Fair value	0	0
Restricted Deposits \| Level III \| Corporate securities
Investments:
Fair value	0	0
Restricted Deposits \| Level III \| Municipal securities
Investments:
Fair value	0	0
Restricted Deposits \| Level III \| Cash and cash equivalents
Investments:
Fair value	0	0
Restricted Deposits \| Level III \| Certificates of deposit
Investments:
Fair value	$ 0	$ 0

Fair value portion of asset recognized for present right to economic benefit.

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Fair value, after the effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and not elected to be offset.

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Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

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