Accumulated Other Comprehensive Income AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	$ 145	$ 130
Other comprehensive income (loss), net before reclassifications	1	65
Tax expense (benefit)		1
Ending Balance	146	192
Equity Method Investments
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	(4)	(3)
Other comprehensive income (loss), net before reclassifications	1	(1)
Tax expense (benefit)		0
Ending Balance	(3)	(4)
Pension and Retiree Health and Welfare Benefit Items
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	149	133
Other comprehensive income (loss), net before reclassifications	0	66
Tax expense (benefit)		1
Ending Balance	$ 149	196
Amortization of net gain
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Before Tax		(1)
Amortization of net gain | Equity Method Investments
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Before Tax		0
Amortization of net gain | Pension and Retiree Health and Welfare Benefit Items
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Before Tax		(1)
Amortization of prior service costs/ credits
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Before Tax		(3)
Amortization of prior service costs/ credits | Equity Method Investments
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Before Tax		0
Amortization of prior service costs/ credits | Pension and Retiree Health and Welfare Benefit Items
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Before Tax		$ (3)