Accumulated Other Comprehensive Income AOCI by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	$ 130	$ 231
Other comprehensive (loss) before reclassifications	65	1
Tax expense (benefit)	1
Ending Balance	192	257
Accounting Standards Update 2016-01
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Net of tax		1
Accounting Standards Update 2018-02
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Net of tax		(26)
Equity Method Investments
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	(3)	(3)
Other comprehensive (loss) before reclassifications	(1)	1
Tax expense (benefit)	0
Ending Balance	(4)	(3)
Equity Method Investments | Accounting Standards Update 2016-01
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Net of tax		1
Equity Method Investments | Accounting Standards Update 2018-02
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Net of tax		0
Pension and Retiree Health and Welfare Benefit Items
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	133	234
Other comprehensive (loss) before reclassifications	66	0
Tax expense (benefit)	1
Ending Balance	196	260
Pension and Retiree Health and Welfare Benefit Items | Accounting Standards Update 2016-01
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Net of tax		0
Pension and Retiree Health and Welfare Benefit Items | Accounting Standards Update 2018-02
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Reclassification from AOCI, Net of tax		$ (26)
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)