Reclassifications out of Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	$ 3,920
Balance at end of period	4,182
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	5	(59)
Amounts reclassified from accumulated other comprehensive loss	0	1
Balance at end of period	(941)	(952)
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	1	22
Amounts reclassified from accumulated other comprehensive loss	47	37
Balance at end of period	(3,023)	(3,226)
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	3	9
Amounts reclassified from accumulated other comprehensive loss	(8)	(11)
Balance at end of period	2	10
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	1
Amounts reclassified from accumulated other comprehensive loss	0	0
Balance at end of period	0	37
Total
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(4,010)	(4,131)
Other comprehensive income (loss) before reclassifications	9	(27)
Amounts reclassified from accumulated other comprehensive loss	39	27
Balance at end of period	$ (3,962)	$ (4,131)