Reclassifications out of Accumulated Other Comprehensive Loss - Changes in Accumulated Other Comprehensive Loss by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	$ 3,920
Balance at end of period	4,104
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	53	(63)
Amounts reclassified from accumulated other comprehensive loss	0	0
Balance at end of period	(893)	(957)
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	0	0
Amounts reclassified from accumulated other comprehensive loss	16	18
Balance at end of period	(3,055)	(3,267)
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	(6)	11
Amounts reclassified from accumulated other comprehensive loss	(3)	(4)
Balance at end of period	(2)	19
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	7
Amounts reclassified from accumulated other comprehensive loss	0	0
Balance at end of period	0	43
Parent and Non-Redeemable Non-Controlling Interest
Changes in Accumulated Other Comprehensive Loss [Roll Forward]
Balance at beginning of period	(4,010)	(4,131)
Other comprehensive income (loss) before reclassifications	47	(45)
Amounts reclassified from accumulated other comprehensive loss	13	14
Balance at end of period	$ (3,950)	$ (4,162)