Investments (Variable Interest Entities) (Details) - USD ($)	1 Months Ended
	Jan. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Other assets		$ 426,800,000	$ 359,700,000
Liabilities		25,834,300,000	25,611,000,000.0
Debt		1,136,600,000	$ 1,067,000,000.0
Variable Interest Entity, Classification
Variable Interest Entity [Line Items]
Payments to acquire business	$ 40,000,000.0
Other assets		166,100,000
Liabilities		126,700,000
Accounts Payable		57,700,000
Debt		69,000,000.0
Line of Credit | Variable Interest Entity, Classification
Variable Interest Entity [Line Items]
Long-term Line of Credit		$ 350,000,000.0