Shareholders' Narrative (Details) - USD ($) shares in Thousands, $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Schedule of Equity Method Investments [Line Items]
Other Comprehensive Income (Loss), Securities, Available-for-Sale, Unrealized Holding Gain (Loss) Arising During Period, Tax	$ 84.0	$ (37.0)
Liquidation preference of preferred stock (per share)	$ 1,000
Preferred stock, authorized shares	4,400	4,400
Carrying value, Preferred stock	$ 566.0	$ 566.0
Warrants sold		5,800
Bank common stock repurchased, shares	23,500	12,900
Treasury Stock Acquired, Average Cost Per Share	$ 46.80	$ 51.77
Net Shares Issued From Stock Warrant Exercises		1,800
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 75.0
Common Stock Shares Outstanding millions	165,100
Total invested assets of trusts	$ 113.0	$ 93.0
Total obligations of trusts	126.0	107.0
Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Tax	10.0	1.0
Other Comprehensive (Income) Loss, Defined Benefit Plan, after Reclassification Adjustment, Tax	$ 2.0	0.0
Preferred stock, liquidation preference per depositary share	$ 25
Common Stock Held in Trust	$ 13.0	13.0
Warrant conversion rate	$ 1.08
Depositary Share, Preferred Stock Ownership Interest	1/40
Effect of Change in Tax Rate, OCI	$ 0.0	0.0
Accumulated Other Comprehensive Income (Loss), Net of Tax	43.0	(250.0)
Stock Repurchased During Period, Value	$ 1,100.0	$ 670.0
Percent adjustments to paid in capital for period	28.00%
Warrants and Rights Outstanding	$ 29.3
Investment Warrants, Exercise Price	$ 33.91
Common Stock [Member]
Schedule of Equity Method Investments [Line Items]
Bank common stock repurchased, shares	23,531	12,984
Net Shares Issued From Stock Warrant Exercises	8	1,770