Accumulated Other Comprehensive Income (Loss) Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Jan. 01, 2018
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period	$ (318.4)	$ (319.9)
Balance, as of January 1, 2018	(318.4)	(319.9)	$ (316.9)
Other comprehensive income loss before reclassifications	(24.4)	1.0
Amounts reclassified from accumulated other comprehensive income loss	37.4	(6.3)
Net current period other comprehensive income loss	13.0	(5.3)
Balance, as of the end of the period	(303.9)	(325.2)
Accumulated Net Unrealized Investment Gain (Loss)
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period	(1.6)	(10.8)
Balance, as of January 1, 2018	(1.6)	(10.8)	(0.1)
Other comprehensive income loss before reclassifications	(8.2)	(2.0)
Amounts reclassified from accumulated other comprehensive income loss	6.0	0.4
Net current period other comprehensive income loss	(2.2)	(1.6)
Balance, as of the end of the period	(2.3)	(12.4)
Accumulated Net Gain (Loss) from Designated or Qualifying Cash Flow Hedges
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period	(104.5)	57.8
Balance, as of January 1, 2018	(104.5)	57.8	(104.5)
Cumulative effect of new accounting principle			0.0
Other comprehensive income loss before reclassifications	(60.4)	(17.1)
Amounts reclassified from accumulated other comprehensive income loss	31.4	(6.7)
Net current period other comprehensive income loss	(29.0)	(23.8)
Balance, as of the end of the period	(133.5)	34.0
Accumulated Defined Benefit Plans Adjustment
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period	(36.8)	(32.7)
Balance, as of January 1, 2018	(36.8)	(32.7)	(36.8)
Cumulative effect of new accounting principle			0.0
Other comprehensive income loss before reclassifications	(0.5)	0.1
Amounts reclassified from accumulated other comprehensive income loss	0.0	0.0
Net current period other comprehensive income loss	(0.5)	0.1
Balance, as of the end of the period	(37.3)	(32.6)
Accumulated Translation Adjustment
Accumulated other comprehensive income [Line Items]
Balance, as of the beginning of the period	(175.5)	(334.2)
Balance, as of January 1, 2018	(175.5)	(334.2)	(175.5)
Cumulative effect of new accounting principle			0.0
Other comprehensive income loss before reclassifications	44.7	20.0
Amounts reclassified from accumulated other comprehensive income loss	0.0	0.0
Net current period other comprehensive income loss	44.7	20.0
Balance, as of the end of the period	$ (130.8)	$ (314.2)
Accounting Standards Update 2016-01
Accumulated other comprehensive income [Line Items]
Cumulative effect of new accounting principle			1.5
Accounting Standards Update 2016-01 | Accumulated Net Unrealized Investment Gain (Loss)
Accumulated other comprehensive income [Line Items]
Cumulative effect of new accounting principle			$ 1.5