Pledged Assets (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 39,600,000,000		$ 39,600,000,000		$ 35,800,000,000
Fair value of accepted collateral	1,600,000,000		1,600,000,000		1,500,000,000
Amount of securities re pledged or sold collateral	0		0		0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	2,300,000,000	$ 1,700,000,000	0	$ 1,600,000,000
US Government Agencies Debt Securities And Other Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	28,600,000,000		28,600,000,000		27,100,000,000
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	772,800,000		772,800,000		117,500,000
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	10,200,000,000		10,200,000,000		8,600,000,000
Collateral Requirements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	7,900,000,000		7,900,000,000		8,900,000,000
Securities Available for Sale
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 1,200,000,000		$ 1,200,000,000		$ 1,500,000,000