Valuation and Qualifying Accounts (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Valuation Allowance of Deferred Tax Assets [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation Allowances and Reserves, Balance, Beginning Balance	$ 133.4	$ 127.1	$ 112.0
Valuation Allowances and Reserves, Charged to Cost and Expense	88.5	11.0	23.7
Valuation Allowances and Reserves, Charged to Other Accounts	10.6	(4.7)	(8.6)
Valuation Allowances and Reserves, Deductions	5.6	0.0	0.0
Valuation Allowances and Reserves, Balance, Ending Balance	226.9	133.4	127.1
Allowance for Loan and Lease Losses, Real Estate [Member]
Movement in Valuation Allowances and Reserves [Roll Forward]
Valuation Allowances and Reserves, Balance, Beginning Balance	7.7	6.8	6.5
Valuation Allowances and Reserves, Charged to Cost and Expense	1.7	0.9	0.3
Valuation Allowances and Reserves, Charged to Other Accounts	0.0	0.0	0.0
Valuation Allowances and Reserves, Deductions	0.0	0.0	0.0
Valuation Allowances and Reserves, Balance, Ending Balance	$ 9.4	$ 7.7	$ 6.8