Reclassifications out of Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	$ 4,725	$ 4,142
Balance at end of period	4,960	4,332
AOCI Attributable to Parent [Member]
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(4,198)	(4,010)
Other comprehensive income (loss) before reclassifications	76	47
Amounts reclassified from accumulated other comprehensive loss	19	13
Balance at end of period	(4,103)	(3,950)
Foreign Currency Translation Adjustment
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(1,155)	(946)
Other comprehensive income (loss) before reclassifications	78	53
Amounts reclassified from accumulated other comprehensive loss	0	0
Balance at end of period	(1,077)	(893)
Unrecognized Net Actuarial Losses and Prior Service Costs
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(3,053)	(3,071)
Other comprehensive income (loss) before reclassifications	4	0
Amounts reclassified from accumulated other comprehensive loss	20	16
Balance at end of period	(3,029)	(3,055)
Deferred Derivative Gains (Losses)
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	10	7
Other comprehensive income (loss) before reclassifications	(6)	(6)
Amounts reclassified from accumulated other comprehensive loss	(1)	(3)
Balance at end of period	$ 3	$ (2)