Fair Value Measurements (Changes in the Balances of Level 3 Financial Assets) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	$ 9.5	$ 61.4	$ 10.0	$ 70.1
Transfers into Level 3	0.0	0.0	0.0	0.0
Transfers out of Level 3	0.0	0.0	0.0	0.0
Total gains or losses for the period
Realized in net income	0.0	(38.5)	(0.5)	(47.2)
Unrealized in accumulated other comprehensive income	0.0	0.0	0.0	0.0
Purchases, issues, sales and settlements
Purchases/additions	0.0	0.0	0.0	0.0
Issues	0.0	0.0	0.0	0.0
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Closing balance	9.5	22.9	9.5	22.9
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0.0	0.0	0.0	0.0
Embedded Contractual Derivative Asset [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	9.5	11.4	10.0	7.2
Transfers into Level 3	0.0	0.0	0.0	0.0
Transfers out of Level 3	0.0	0.0	0.0	0.0
Total gains or losses for the period
Realized in net income	0.0	1.9	(0.5)	6.1
Unrealized in accumulated other comprehensive income	0.0	0.0	0.0	0.0
Purchases, issues, sales and settlements
Purchases/additions	0.0	0.0	0.0	0.0
Issues	0.0	0.0	0.0	0.0
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Closing balance	9.5	13.3	9.5	13.3
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0.0	0.0	0.0	0.0
Other Noncurrent Assets [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Opening balance	0.0	50.0	0.0	62.9
Transfers into Level 3	0.0	0.0	0.0	0.0
Transfers out of Level 3	0.0	0.0	0.0	0.0
Total gains or losses for the period
Realized in net income	0.0	(40.4)	0.0	(53.3)
Unrealized in accumulated other comprehensive income	0.0	0.0	0.0	0.0
Purchases, issues, sales and settlements
Purchases/additions	0.0	0.0	0.0	0.0
Issues	0.0	0.0	0.0	0.0
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Closing balance	0.0	9.6	0.0	9.6
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 0.0	$ 0.0	$ 0.0	$ 0.0