Pledged Assets (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 34,100,000,000		$ 34,100,000,000		$ 32,300,000,000
Fair value of accepted collateral	1,200,000,000		1,200,000,000		1,000,000,000
Amount of securities repledged or sold collateral	0		0		0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	1,700,000,000	$ 1,300,000,000	1,600,000,000	$ 1,300,000,000
US Government Agencies Debt Securities And Other Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	24,900,000,000		24,900,000,000		23,100,000,000
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	97,600,000		97,600,000		122,900,000
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	9,100,000,000		9,100,000,000		9,100,000,000
Collateral Requirements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	8,500,000,000		8,500,000,000		5,900,000,000
Securities Available for Sale
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 982,400,000		$ 982,400,000		$ 884,800,000