Securities (Details 2) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Dec. 31, 2011	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Cumulative Credit Portion of Impairments on Debt Securities
Cumulative Impairments on Debt Securities, Beginning Balance	$ 4
Impairment recognized in earnings	0
Cumulative Impairments on Debt Securities, Ending Balance	4	4
Available for Sale Securities Realized Gains and Losses
Realized gains		23	19	129
Realized losses		22	5	16
Net securities gains (losses)		1	14	113
Securities by Maturity
Amortized cost of securities available for sale, Due in one year or less	649	649
Amortized cost of securities available for sale, Due after one through five years	14,761	14,761
Amortized cost of securities available for sale, Due after five through ten years	71	71
Amortized cost of securities available for sale, Due after ten years	9	9
Total amortized cost of securities available for sale	15,490	15,490
Fair Value of securities available for sale, Due in one year or less	663	663
Fair Value of securities available for sale, Due after one through five years	15,263	15,263
Fair Value of securities available for sale, Due after five through ten years	76	76
Fair Value of securities available for sale, Due after ten years	10	10
Total Fair Value of securities available for sale	16,012	16,012
Amortized cost of held-to-maturity securities, Due in one year or less	9	9
Amortized cost of held-to-maturity securities, Due after one through five years	2,100	2,100
Amortized cost of held-to-maturity securities, Due after five through ten years	0	0
Amortized cost of held-to-maturity securities, Due after ten years	0	0
Total amortized cost of held-to-maturity securities	2,109	2,109
Fair Value of held-to-maturity securities, Due in one year or less	9	9
Fair Value of held-to-maturity securities, Due after one through five years	2,124	2,124
Fair Value of held-to-maturity securities, Due after five through ten years	0	0
Fair Value of held-to-maturity securities, Due after ten years	0	0
Total Fair Value of held-to-maturity securities	$ 2,133	$ 2,133

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