Accumulated Other Comprehensive Income AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2026	Mar. 31, 2025
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	$ 498	$ 581
Other comprehensive income (loss), net before reclassifications	(1)	1
Reclassification from AOCI, Current Period, Tax	2	2
Ending Balance	493	576
Equity Method Investments
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	9	9
Other comprehensive income (loss), net before reclassifications	(1)	1
Reclassification from AOCI, Current Period, Tax	0	0
Ending Balance	8	10
Pension and Retiree Health and Welfare Benefit Items
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	489	572
Other comprehensive income (loss), net before reclassifications	0	0
Reclassification from AOCI, Current Period, Tax	2	2
Ending Balance	485	566
Amortization of net (gains) losses
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Amortization of actuarial (gains) losses	(6)	(8)
Amortization of net (gains) losses | Equity Method Investments
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Amortization of actuarial (gains) losses	0	0
Amortization of net (gains) losses | Pension and Retiree Health and Welfare Benefit Items
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Amortization of actuarial (gains) losses	$ (6)	$ (8)