Accumulated Other Comprehensive Income AOCI by Component (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Balance		$ 43,009	$ 36,172
Balance		36,172	35,032
Equity Method Investee [Member]
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Balance		(3)	(3)
Other Comprehensive Income (Loss), before Reclassifications		0	(1)
Amounts reclassified from AOCI		0	0
Balance		(3)	(2)
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 Income (Loss), before Reclassifications	[1]	114	73
Amounts reclassified from AOCI	[1],[2]	(2)	(1)
Balance	[1]	122	50
Accumulated Other Comprehensive Income (Loss) [Member]
Other Comprehensive Income (Loss) Net of Tax, Period Change [Abstract]
Balance		231	119
Other Comprehensive Income (Loss), before Reclassifications		114	72
Amounts reclassified from AOCI		(2)	(1)
Balance		$ 119	$ 48

[1] Amounts are net of tax. See Note 13 to the Consolidated Financial Statements for additional details.

[2] Amounts in parenthesis indicate debits to the income statement.