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Investment Securities (Details 6) (USD $)
In Millions, unless otherwise specified
3 Months Ended 6 Months Ended
Jun. 30, 2012
Jun. 30, 2011
Jun. 30, 2012
Jun. 30, 2011
Summary of credit losses on debt securities (excluding perpetual preferred securities)        
Balance at beginning of period $ 288 $ 339 $ 298 $ 358
Additions to credit losses due to other-than-temporary impairments        
Credit losses on securities not previously considered other-than-temporarily impaired 2 1 3 2
Decreases in expected cash flows on securities for which other-than-temporary impairment was previously recognized 11 8 19 13
Total other-than-temporary impairment on debt securities 13 9 22 15
Other changes in credit losses        
Increases in expected cash flows (8) (10) (14) (17)
Realized losses (a) (16) (19) (29) (36)
Credit losses on security sales and securities expected to be sold       (1)
Balance at end of period $ 277 $ 319 $ 277 $ 319