Investments (Narrative) (Detail) $ in Millions |
3 Months Ended | 12 Months Ended |
|---|---|---|
|
Mar. 31, 2023
USD ($)
security
|
Dec. 31, 2022
USD ($)
security
|
|
| Schedule Of Investments [Line Items] | ||
| Fair value of securities on deposit with various regulatory authorities | $ | $ 10 | $ 10 |
| Number of securities in unrealized loss position for a continuous 12 month period | security | 495 | 210 |
| Rate that a security's fair value is below book value | 5.00% | 5.00% |
| Asset Pledged as Collateral [Member] | ||
| Schedule Of Investments [Line Items] | ||
| Fair value of securities pledged as collateral | $ | $ 228 | $ 251 |
| Securities In Unrealized Loss Position [Member] | ||
| Schedule Of Investments [Line Items] | ||
| Weighted average contractual maturity period in years for securities in an unrealized loss position | 14 years | 14 years |
| Fair Value Below Book Value Greater Than Five Percent [Member] | ||
| Schedule Of Investments [Line Items] | ||
| Number of securities in unrealized loss position for a continuous 12 month period | security | 444 | 190 |