Accumulated Other Comprehensive Income AOCI by Component (Details) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance				$ 231	$ 119
Other comprehensive (loss) before reclassifications				1	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[1]	$ (1)	$ 0	24	(1)
Ending Balance		256	117	256	117
Equity Method Investee [Member]
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance				(3)	(3)
Other comprehensive (loss) before reclassifications				1	(1)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax				(1)	0
Ending Balance		(3)	(4)	(3)	(4)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Beginning Balance	[2]			234	122
Other comprehensive (loss) before reclassifications	[2]			0	0
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	[2]			25	(1)
Ending Balance	[2]	$ 259	$ 121	$ 259	$ 121

[1] Amounts in parentheses indicate debits to the income statement.

[2] Amounts are net of tax.