Accumulated Other Comprehensive Income (Loss) - After-tax Changes by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	$ (3,778)	$ (2,728)
Amounts arising during the period	(30)	(384)
Reclassifications from accumulated other comprehensive income	31	(47)
Net other comprehensive income during the period	1	(431)
Balance at end of period	(3,777)	(3,159)
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1,627)	(520)
Amounts arising during the period	(24)	(464)
Reclassifications from accumulated other comprehensive income	0	0
Net other comprehensive income during the period	(24)	(464)
Balance at end of period	(1,651)	(984)
Qualifying Derivatives Unrealized Gains (Losses) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(7)	(7)
Amounts arising during the period	(6)	80
Reclassifications from accumulated other comprehensive income	(1)	(78)
Net other comprehensive income during the period	(7)	2
Balance at end of period	(14)	(5)
Equity Investees Accumulated Other Comprehensive Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(1)	0
Amounts arising during the period	0	0
Reclassifications from accumulated other comprehensive income	0	0
Net other comprehensive income during the period	0	0
Balance at end of period	(1)	0
Defined Benefit Plans Prior Service Costs [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(8)	(6)
Amounts arising during the period	0	0
Reclassifications from accumulated other comprehensive income	0	0
Net other comprehensive income during the period	0	0
Balance at end of period	(8)	(6)
Defined Benefit Plans Actuarial Gain (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Balance at beginning of period	(2,135)	(2,195)
Amounts arising during the period	0	0
Reclassifications from accumulated other comprehensive income	32	31
Net other comprehensive income during the period	32	31
Balance at end of period	$ (2,103)	$ (2,164)