Accumulated Other Comprehensive Income (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance	$ 7,880	$ 5,236
Other comprehensive income (loss) before reclassification, net of tax	2	286
Amounts reclassifed from accumulated OCI, net of tax	(216)	(178)
Net other comprehensive income (loss), net of tax	(214)	108
Accumulated other comprehensive income, ending balance	7,666	5,344
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance	(367)	(284)
Other comprehensive income (loss) before reclassification, net of tax	(20)	121
Amounts reclassifed from accumulated OCI, net of tax	25	0
Net other comprehensive income (loss), net of tax	5	121
Accumulated other comprehensive income, ending balance	(362)	(163)
Net Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance	450	272
Other comprehensive income (loss) before reclassification, net of tax	16	75
Amounts reclassifed from accumulated OCI, net of tax	(11)	(7)
Net other comprehensive income (loss), net of tax	5	68
Accumulated other comprehensive income, ending balance	455	340
Net Unrealized Gains (Losses) on Cash Flow Hedges [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance	445	(110)
Other comprehensive income (loss) before reclassification, net of tax	6	90
Amounts reclassifed from accumulated OCI, net of tax	7	7
Net other comprehensive income (loss), net of tax	13	97
Accumulated other comprehensive income, ending balance	458	(13)
Defined Benefit Postretirement Plans [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Accumulated other comprehensive income, beginning balance	7,352	5,358
Other comprehensive income (loss) before reclassification, net of tax	0	0
Amounts reclassifed from accumulated OCI, net of tax	(237)	(178)
Net other comprehensive income (loss), net of tax	(237)	(178)
Accumulated other comprehensive income, ending balance	$ 7,115	$ 5,180