Accumulated Other Comprehensive Income AOCI by Component (Details) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2018	Mar. 31, 2017
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Balance		$ 43,009
Balance		43,052
Equity Method Investee [Member]
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Balance		(3)	$ (3)
Other comprehensive (loss) before reclassifications		1	(2)
Amounts reclassified from AOCI		(1)	0
Balance		(3)	(5)
Accumulated Defined Benefit Plans Adjustment Attributable to Parent [Member]
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Balance	[1]	234	122
Other comprehensive (loss) before reclassifications	[1]	0	0
Amounts reclassified from AOCI	[1]	26	0
Balance	[1]	260	122
AOCI Attributable to Parent [Member]
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Balance		231	119
Other comprehensive (loss) before reclassifications		1	(2)
Amounts reclassified from AOCI		25	0
Balance		$ 257	$ 117

[1] Amounts are net of tax.