Accumulated Other Comprehensive Income Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning balance		$ 119	$ 48
Other Comprehensive Income (Loss) before Reclassifications		(2)	(2)
Accumulated Other Comprehensive Income (Loss), Ending balance		117	46
Pension and Retiree Health and Welfare Benefit Items [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning balance	[1]	122	50
Other Comprehensive Income (Loss) before Reclassifications	[1]	0	0
Accumulated Other Comprehensive Income (Loss), Ending balance	[1]	122	50
Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts reclassified from AOCI		0	0
Reclassification out of Accumulated Other Comprehensive Income [Member] | Pension and Retiree Health and Welfare Benefit Items [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts reclassified from AOCI	[1]	0	0
Equity Method Investee [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Accumulated Other Comprehensive Income (Loss), Beginning balance		(3)	(2)
Other Comprehensive Income (Loss) before Reclassifications		(2)	(2)
Accumulated Other Comprehensive Income (Loss), Ending balance		(5)	(4)
Equity Method Investee [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts reclassified from AOCI		$ 0	$ 0

[1] Amounts are net of tax.