Securities - Changes in Credit Loss (Details 4) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Changes in the credit loss component of credit-impaired debt securities, securities with no intent to sell [Abstract]
Balance, beginning of period	$ 708	$ 632	$ 578
Additions:
Newly credit-impaired securities	21	4	0
Increase in losses on previously credit-impaired securities	0	0	94
Losses reclassified from other comprehensive income on previously credit-impaired securities	7	72	6
Reductions:
Sales of credit-impaired securities	(214)	0	(31)
Impact of new accounting guidance related to VIEs	0	0	(15)
Balance, end of period	$ 522	$ 708	$ 632

Amount of the effect of a change in accounting principle on net income.

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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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- Definition

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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