Business And Summary Of Significant Accounting Policies (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2017 USD ($)	Sep. 30, 2017 USD ($)	Jun. 30, 2017 USD ($)	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2017 USD ($) branch	Dec. 31, 2016 USD ($) payment	Dec. 31, 2015 USD ($)	Aug. 03, 2015 USD ($)
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Number of branches acquired | branch									70
Period past due when loans go into non accrual status									90 days
Number of consecutive scheduled payments for TDRs to remain reasonably assured | payment										6
Minimum value of loans to be individually assessed for impairment	$ 500,000								$ 500,000
Period for which loans are considered past due									30 days
Net income (loss) before attribution of noncontrolling interests	(88,000,000)	$ 219,600,000	$ 156,700,000	$ 179,900,000	$ (1,142,500,000)	$ 131,500,000	$ 17,000,000	$ 146,000,000	$ 468,200,000	$ (848,000,000)	$ 1,034,000,000
Non-interest income									1,371,600,000	1,182,200,000	1,167,700,000
Provision for income taxes	27,700,000	$ (119,800,000)	$ (31,900,000)	$ 56,200,000	(6,600,000)	$ 54,500,000	$ 111,200,000	$ 44,400,000	(67,800,000)	203,500,000	(538,000,000)
Tax credit investments and investments in unconsolidated subsidiaries	247,600,000				220,200,000				247,600,000	220,200,000
Current and deferred federal and state tax assets	205,200,000				$ 201,300,000				$ 205,200,000	201,300,000
Servicing advances, threshold period for allowance									180 days
Net cash flows provided by operations									$ 519,800,000	2,399,200,000	1,189,800,000
Increase in other assets									(170,200,000)	(230,100,000)	(53,300,000)
Decrease in accrued liabilities and payables									(715,600,000)	258,600,000	(45,100,000)
Net cash flows used in investing activities									$ 7,755,200,000	(495,300,000)	$ 1,085,200,000
Prepaid Railcar Certification Costs
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Estimated useful life									10 years
Adoption of Proportional Amortization Method
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Net income (loss) before attribution of noncontrolling interests	(8,800,000)
Non-interest income	29,400,000
Provision for income taxes	38,200,000
Tax credit investments and investments in unconsolidated subsidiaries	(10,500,000)								$ (10,500,000)
Current and deferred federal and state tax assets	1,800,000								$ 1,800,000
Adjustment
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Net cash flows provided by operations										(3,600,000)
Increase in other assets										935,000,000
Decrease in accrued liabilities and payables										936,400,000
Net cash flows used in investing activities										$ (3,600,000)
Minimum | Furniture, Fixtures and Equipment
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Service lives									3 years
Minimum | Buildings
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Service lives									20 years
Maximum | Furniture, Fixtures and Equipment
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Service lives									7 years
Maximum | Buildings
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Service lives									40 years
Commercial Banking
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Minimum value of loans to be individually assessed for impairment	$ 500,000								$ 500,000
Reverse Mortgage
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Period for which company will establish an allowance if borrower does not occupy residence									12 months
Small Commercial Loans
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Period past due when loans go into non accrual status									90 days
Small Commercial Loans | Minimum
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Delinquency period for loan charge offs									90 days
Small Commercial Loans | Maximum
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Delinquency period for loan charge offs									180 days
Consumer Loans
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Delinquency period for loan charge offs									120 days
Consumer and Small Commercial Borrower | Mortgages, Commercial Loans and Leases
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Period past due when loans go into non accrual status									90 days
Repayment period when loans are reclassified from non accrual status									6 months
OneWest Bank
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Duration of acquisition activity reported										5 months
Allowance for credit losses												$ 0