Acquisitions (Narratives) (Details) (USD $)	0 Months Ended	3 Months Ended				0 Months Ended	3 Months Ended	0 Months Ended	3 Months Ended	12 Months Ended
	Feb. 17, 2012	Mar. 31, 2012	Sep. 30, 2011	Mar. 31, 2011	Dec. 31, 2011	Feb. 16, 2012 Forward Purchasers [Member]	Sep. 30, 2011 Forward Sale Agreements [Member]	Jun. 16, 2011 ING Direct Bancorporation [Member]	Mar. 31, 2012 ING Direct Bancorporation [Member]	Dec. 31, 2011 ING Direct Bancorporation [Member]
Acquisitions [Line Items]
Deposits added relating to acquisition of ING Direct		$ 216,528,000,000			$ 128,226,000,000			$ 84,400,000,000
Number of customers added relating to acquisition of ING Direct								7,000,000
Issuance of common stock in exchange for the equity interest and assets and liabilities, shares	54,028,086
Issuance of common stock in exchange for the equity interest and assets and liabilities, value	2,600,000,000
Cash consideration in exchange for the equity interests and assets and liabilities	6,300,000,000
Closure of public underwritten offering, shares							40,000,000
Deferred direct cost relating to equity offering			73,000,000
Cash proceeds relating to closure of public offering			3,000,000,000			1,900,000,000
Transaction costs related to ING Direct acquisition		2,504,000,000		2,162,000,000					62,000,000
Components of other non-interest expense		846,000,000		727,000,000					37,000,000	25,000,000
Fair value of net assets acquired from ING Direct		9,600,000,000
Bargain purchase gain	594,000,000	594,000,000		0
ING Direct purchase price		$ 9,000,000,000