Benefit Plans: (Pension and Other Employee Benefit Costs) (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Defined Benefit Plan Disclosure [Line Items]
Total pension and other employee benefit costs	$ 60	$ 45	$ 24
Pension
Defined Benefit Plan Disclosure [Line Items]
Total pension and other employee benefit costs	(76)	(84)	(93)
Post- employment
Defined Benefit Plan Disclosure [Line Items]
Total pension and other employee benefit costs	123	117	107
Post- retirement
Defined Benefit Plan Disclosure [Line Items]
Total pension and other employee benefit costs	$ 13	$ 12	$ 10

Amount of expense (reversal of expense) for net periodic benefit cost components, excluding service cost component, of defined benefit plan. Amount includes, but is not limited to, interest cost, expected (return) loss on plan asset, amortization of prior service cost (credit), amortization of (gain) loss, amortization of transition (asset) obligation, settlement (gain) loss, curtailment (gain) loss and certain termination benefits.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 715
-SubTopic 20
-Name Accounting Standards Codification
-Section 45
-Paragraph 3A
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480535/715-20-45-3A

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration