Other Comprehensive Income and Accumulated Other Comprehensive Income (details) - Reclassifications (USD $) In Millions, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Income tax (expense) benefit	$ 7	$ 306	$ 109	$ 271	$ 160	$ (1)	$ (363)	$ 130	$ 693	$ (74)	$ 1,090
Amounts reclassified from accumulated other comprehensive income, net of taxes									14	(21)	(161)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive income, before tax									21	(33)	(252)
Income tax (expense) benefit									7	(12)	(91)
Amounts reclassified from accumulated other comprehensive income, net of taxes									14	(21)	(161)
Changes in Net Unrealized Gains on Investment Securities Having No Credit Losses Recognized in the Consolidated Statement of Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive income, net of taxes									(49)	(81)	(207)
Changes in Net Unrealized Gains on Investment Securities Having No Credit Losses Recognized in the Consolidated Statement of Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive income, before tax									(75)	(125)	(318)
Income tax (expense) benefit									(26)	(44)	(111)
Amounts reclassified from accumulated other comprehensive income, net of taxes									(49)	(81)	(207)
Changes in Net Unrealized Gains on Investment Securities Having Credit Losses Recognized in the Consolidated Statement of Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive income, net of taxes									5	10	6
Changes in Net Unrealized Gains on Investment Securities Having Credit Losses Recognized in the Consolidated Statement of Income [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive income, before tax									8	16	9
Income tax (expense) benefit									3	6	3
Amounts reclassified from accumulated other comprehensive income, net of taxes									5	10	6
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive income, net of taxes									58	50	40
Net Benefit Plan Assets and Obligations Recognized in Shareholders' Equity [Member] | Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income
Amounts reclassified from accumulated other comprehensive income, before tax									88	76	57
Income tax (expense) benefit									30	26	17
Amounts reclassified from accumulated other comprehensive income, net of taxes									$ 58	$ 50	$ 40