Other Assets (Components Of Other Assets) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule Of Other Assets [Line Items]
Tax credit investments and investments in unconsolidated subsidiaries	$ 247,600,000	$ 220,200,000
Counterparty receivables	241,300,000	437,300,000
Current and deferred federal and state tax assets	205,200,000	201,300,000
Property, furniture and fixtures	173,900,000	191,100,000
Indemnification assets	142,400,000	341,400,000
Intangible assets	113,000,000	140,700,000
Other	472,100,000	585,000,000
Total other assets	1,595,500,000	2,117,000,000
Affordable housing investments	182,800,000	151,300,000
Pre-tax losses from affodable housing investments		12,100,000
Amortization expense on affordable housing investments	50,800,000	0
Tax benefits from affordable housing investments	29,600,000	20,600,000
Tax credits from affordable housing investments	22,600,000	15,900,000
Liability for unfuded commitments from affordable housing investments	66,600,000	62,300,000
Single Family Mortgage Loans
Schedule Of Other Assets [Line Items]
Loans serviced for others	$ 34,100,000	$ 55,100,000