Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning of year			$ 36,834
Total other comprehensive income (loss)	$ 159	$ (2)	158	$ 39
End of year	34,868		34,868
Foreign Currency
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning of year	(129)	(125)	(127)	(165)
Other comprehensive income (loss) before reclassifications	8	(3)	6	37
Total other comprehensive income (loss)	8	(3)	6	37
End of year	(121)	(128)	(121)	(128)
Losses on Cash Flow Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning of year	(4)	(6)	(5)	(7)
Amounts reclassified from accumulated other comprehensive income		1	1	2
Total other comprehensive income (loss)		1	1	2
End of year	(4)	(5)	(4)	(5)
Pension and Other Postretirement Benefits
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning of year	(173)	(186)	(173)	(186)
Amounts reclassified from accumulated other comprehensive income	151		151
Total other comprehensive income (loss)	151		151
End of year	(22)	(186)	(22)	(186)
Accumulated Other Comprehensive Loss
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning of year	(306)	(317)	(305)	(358)
Other comprehensive income (loss) before reclassifications	8	(3)	6	37
Amounts reclassified from accumulated other comprehensive income	151	1	152	2
Total other comprehensive income (loss)	159	(2)	158	39
End of year	$ (147)	$ (319)	$ (147)	$ (319)