Changes in Accumulated Other Comprehensive Losses (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]
Balance at January 1			$ 146,722	$ 153,886
Components of Other Comprehensive Income (Loss):
Other Comprehensive Gain, Net of Tax	$ 182	$ 189	421	448
Balance at September 30	147,911	147,952	147,911	147,952
Income tax expense	672	$ (192)	1,589	$ (1,803)
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(3,843)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			40
Reclassifications			381
Other Comprehensive Gain, Net of Tax			421
Balance at September 30	(3,422)		(3,422)
Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(162)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			37
Reclassifications			0
Other Comprehensive Gain, Net of Tax			37
Balance at September 30	(125)		(125)
Unrealized Holding Gains (Losses) on Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(2)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			(7)
Reclassifications			0
Other Comprehensive Gain, Net of Tax			(7)
Balance at September 30	(9)		(9)
Derivatives
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, Net of Tax			0
Balance at September 30	(2)		(2)
Defined Benefit Plans
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(3,677)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			10
Reclassifications			381
Other Comprehensive Gain, Net of Tax			391
Balance at September 30	$ (3,286)		(3,286)
Defined Benefit Plans | Reclassification out of Accumulated Other Comprehensive Income
Components of Other Comprehensive Income (Loss):
Employee benefits reclassification component, included in employee benefit costs			594
Income tax expense			$ 213