Changes in Accumulated Other Comprehensive Losses (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	$ 152,716
Components of Other Comprehensive Income (Loss):
Before Reclassifications	(156)
Reclassifications	604
Other Comprehensive Gain (Loss), Net of Tax	448	$ 568	$ (1,280)
Balance at December 31	145,556	152,716
Income tax expense (benefit)	(1,729)	132	11,892
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(4,291)
Components of Other Comprehensive Income (Loss):
Balance at December 31	(3,843)	(4,291)
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(140)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	(22)
Reclassifications	0
Other Comprehensive Gain (Loss), Net of Tax	(22)	(44)	(73)
Balance at December 31	(162)	(140)
Unrealized Holding Gains (Losses) on Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(29)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	27
Reclassifications	0
Other Comprehensive Gain (Loss), Net of Tax	27	(21)	(2)
Balance at December 31	(2)	(29)
Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(2)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	0
Reclassifications	0
Other Comprehensive Gain (Loss), Net of Tax	0	0	(54)
Balance at December 31	(2)	(2)
Defined Benefit Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1	(4,120)
Components of Other Comprehensive Income (Loss):
Before Reclassifications	(161)
Reclassifications	604
Other Comprehensive Gain (Loss), Net of Tax	443	633	$ (1,151)
Balance at December 31	(3,677)	$ (4,120)
Defined Benefit Plans [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Components of Other Comprehensive Income (Loss):
Employee benefits reclassification component, included in employee benefit costs	937
Income tax expense (benefit)	$ 333