Investment Securities (Narrative) (Details) (USD $)	3 Months Ended			12 Months Ended
	Mar. 31, 2012		Mar. 31, 2011	Dec. 31, 2011
Investment Securities [Abstract]
Securities available for sale, at fair value	$ 60,810,000,000			$ 38,759,000,000
Increase in investment securities	22,100,000,000
Percentage of investment securities increase	57.00%
Percentage of portfolio invested in U.S. Treasury and agency securities	72.00%			69.00%
Gross unrealized losses, available-for-sale securities	228,000,000			227,000,000
Number of individual securities that account for gross unrealized losses	979
Investments in non-agency residential MBS and asset-backed securities	174,000,000
Percent of total unrealized losses related to non-agency residential MBS and asset-backed securities	76.00%
Loss position for more than 12 months	125,000,000			169,000,000
Credit related losses in earnings	14,000,000		3,000,000
Gross unrealized losses- OTTI	116,000,000	[1]	111,000,000	170,000,000
Gross unrealized losses related to all other securities	112,000,000			57,000,000
Proceeds from sale of investment securities	7,300,000,000		846,000,000
Net realized gains	11,000,000		3,000,000
Fair value of securities pledged	8,200,000,000		8,800,000,000
Debt securities acquired, fair value	30,200,000,000
Debt securities acquired, outstanding unpaid principal and interest balance	5,600,000,000
Debt securities acquired, estimated fair value			$ 2,900,000,000

[1] Represents the amount of cumulative non-credit other-than-temporary impairment ("OTTI") losses recorded in AOCI. These losses are included in total gross unrealized losses.