Accumulated Other Comprehensive Income Reclassification of Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total before tax									$ (6,169)		$ (5,928)		$ (5,377)
Income Tax (expense) / benefit									2,300		2,135		2,005
Net of tax	(1,194)	(1,035)	(916)	(724)	(1,122)	(989)	(884)	(798)	(3,869)		(3,793)		(3,372)
Pension and Retiree Health and Welfare Benefit Items [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Actuarial losses									(2)	[1],[2]	(22)	[1],[2]
Prior service credits									3	[1],[2]	1	[1],[2]
Total before tax									1	[2]	(21)	[2]
Income Tax (expense) / benefit									0	[2]	7	[2]
Net of tax									$ 1	[2]	$ (14)	[2]

[1] This component is included in the computation of net periodic pension and retiree health and welfare cost (see Note 13 for additional details).

[2] Amounts in parenthesis indicate debits in the income statement.