Changes in Accumulated Other Comprehensive Losses (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			$ (4,291)
Components of Other Comprehensive Income (Loss):
Other Comprehensive Gain, Net of Tax	$ 189	$ 102	448	$ 310
Balance at September 30	(3,843)		(3,843)
Income tax expense	(192)	$ 727	(1,803)	$ 1,787
AOCI Attributable to Parent [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(4,291)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			40
Reclassifications			408
Other Comprehensive Gain, Net of Tax			448
Balance at September 30	(3,843)		(3,843)
Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at January 1			(140)
Components of Other Comprehensive Income (Loss):
Before Reclassifications			9
Reclassifications			0
Other Comprehensive Gain, Net of Tax			9
Balance at September 30	(131)		(131)
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			31
Reclassifications			0
Other Comprehensive Gain, Net of Tax			31
Balance at September 30	2		2
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, Net of Tax			0
Balance at September 30	(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			0
Reclassifications			408
Other Comprehensive Gain, Net of Tax			408
Balance at September 30	$ (3,712)		(3,712)
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			659
Income tax expense			$ 251