Securities Available for Sale and Securities Held to Maturity (Rollforward Amount of Credit Losses Recognized in Earnings for OTTI Securities for Portion of Impairment Recognized in or Reclassified From Other Comprehensive (Loss) Income) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Securities Available for Sale and Securities Held to Maturity [Abstract]
Balance at beginning of period	$ 163	$ 145	$ 159	$ 127
Credit losses recognized into current period earnings on debt securities for which an other-than-temporary impairment was not previously recognized	1	4	1	5
Credit losses recognized into current period earnings on debt securities for which an other-than-temporary impairment was previously recognized	2	3	6	20
Balance at end of period	$ 166	$ 152	$ 166	$ 152