Pledged Assets (Narrative) (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Sep. 29, 2017	Dec. 31, 2016
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	$ 41,800,000,000		$ 41,800,000,000			$ 38,900,000,000
Fair value of accepted collateral	235,400,000		235,400,000			217,500,000
Amount of securities re pledged or sold collateral						0
Average deposits maintained to meet Federal Reserve Bank reserve requirements	4,000,000,000	$ 2,300,000,000	2,700,000,000	$ 2,000,000,000
US Government Agencies Debt Securities And Other Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	32,200,000,000		32,200,000,000			28,300,000,000
Obligations of States and Political Subdivisions
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	806,400,000		806,400,000			939,800,000
Loans
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	8,800,000,000		8,800,000,000			9,600,000,000
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			9,300,000,000
Available for Sale Investment Securities
Financial Instruments Owned and Pledged as Collateral [Line Items]
Amount of securities and loans pledged	520,400,000		520,400,000			494,700,000
Repurchase Agreements
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fair value of accepted collateral	1,400,000,000		1,400,000,000			$ 1,800,000,000
Derivative contract
Financial Instruments Owned and Pledged as Collateral [Line Items]
Fair value of accepted collateral	$ 0		$ 0
Amount of securities re pledged or sold collateral					$ 0