Changes in Accumulated Other Comprehensive Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			$ 149,319	$ 146,722
Components of Other Comprehensive Income (Loss):
Before Reclassifications			(71)
Reclassifications			395
Other Comprehensive Gain, Net of Tax	$ 103	$ 182	324	421
Balance at September 30	154,673	147,911	154,673	147,911
Related income taxes	1,643	$ 672	4,540	$ 1,589
Total
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(3,589)
Components of Other Comprehensive Income (Loss):
Balance at September 30	(3,265)		(3,265)
Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(105)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			(12)
Reclassifications			0
Other Comprehensive Gain, Net of Tax			(12)
Balance at September 30	(117)		(117)
Unrealized Holding Gains (Losses) on Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(5)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			(6)
Reclassifications			0
Other Comprehensive Gain, Net of Tax			(6)
Balance at September 30	(11)		(11)
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			(3,477)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			(53)
Reclassifications			395
Other Comprehensive Gain, Net of Tax			342
Balance at September 30	$ (3,135)		(3,135)
Defined Benefit Plans | Reclassification out of Accumulated Other Comprehensive Income
Components of Other Comprehensive Income (Loss):
Employee Benefits for reclassified components			513
Related income taxes			$ 118