Securities - Changes in Credit Loss (Details 4) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Changes in the credit loss component of credit-impaired debt securities, securities with no intent to sell [Abstract]
Balance, beginning of period	$ 522	$ 708
Newly credit-impaired securities	0	6
Losses reclassified from other comprehensive income on previously credit-impaired securities	0	1
Other than Temporary Impairment, Credit Losses Recognized in Earnings, Reductions, Securities Sold	(3)	0
Balance, end of period	$ 519	$ 715

The cumulative amount of credit losses recognized in earnings related to debt securities held for which a portion of an other than temporary impairment (OTTI) was recognized in other comprehensive income (a component of shareholders' equity).

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This item represents reductions in the amount of cumulative losses recognized in earnings for other than temporary impairments (OTTI) for which a portion of the impairment had been recognized in other comprehensive income (a component of shareholders' equity) due to a change in status of the impaired security because of a change in the entity's intent to either sell the impaired security or it has become more likely than not that the entity will be required to sell the security before recovery of its cost basis.

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