Reclassifications out of Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	$ 3,920
Balance at end of period	4,477
Foreign Currency Translation Adjustment
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(946)	$ (894)
Other comprehensive income (loss) before reclassifications	(7)	(140)
Amounts reclassified from accumulated other comprehensive loss	0	2
Balance at end of period	(953)	(1,032)
Unrecognized Net Actuarial Losses and Prior Service Costs
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(3,071)	(3,285)
Other comprehensive income (loss) before reclassifications	2	22
Amounts reclassified from accumulated other comprehensive loss	64	55
Balance at end of period	(3,005)	(3,208)
Deferred Derivative Gains (Losses)
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	7	12
Other comprehensive income (loss) before reclassifications	(1)	14
Amounts reclassified from accumulated other comprehensive loss	(5)	(17)
Balance at end of period	1	9
Unrealized Investment Gains
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	0	36
Other comprehensive income (loss) before reclassifications	0	(3)
Amounts reclassified from accumulated other comprehensive loss	0	0
Balance at end of period	0	33
Total
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(4,010)	(4,131)
Other comprehensive income (loss) before reclassifications	(6)	(107)
Amounts reclassified from accumulated other comprehensive loss	59	40
Balance at end of period	$ (3,957)	$ (4,198)