Accumulated Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance	$ (299.0)	$ (135.2)
Balance, January 1, 2018	(299.0)	(149.3)
Other comprehensive income (loss), before reclassifications, net of tax	103.3	0.7
Amounts reclassified from accumulated other comprehensive income, net of tax	21.4	(14.8)
Other comprehensive income (loss), net of tax	125.4	(13.5)
Accumulated other comprehensive income (loss), net of tax ending balance	(174.3)	(149.3)
Other comprehensive income (loss), net of tax	124.7	(14.1)
Unrealized gains (losses) on securities available for sale
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance	1.4	4.2
Balance, January 1, 2018	0.6	(3.6)
Other comprehensive income (loss), before reclassifications, net of tax	(1.2)	(20.8)
Amounts reclassified from accumulated other comprehensive income, net of tax	0.4	13.0
Other comprehensive income (loss), net of tax	(0.8)	(7.8)
Accumulated other comprehensive income (loss), net of tax ending balance	0.6	(3.6)
Unrealized gains (losses) on cash flow hedges
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance	(179.0)	7.8
Balance, January 1, 2018	(29.4)	41.6
Other comprehensive income (loss), before reclassifications, net of tax	128.6	60.7
Amounts reclassified from accumulated other comprehensive income, net of tax	21.0	(26.9)
Other comprehensive income (loss), net of tax	149.6	33.8
Accumulated other comprehensive income (loss), net of tax ending balance	(29.4)	41.6
Gains (losses) on net investment hedge
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance	(8.5)	25.1
Balance, January 1, 2018	13.9	48.1
Other comprehensive income (loss), before reclassifications, net of tax	22.4	23.9
Amounts reclassified from accumulated other comprehensive income, net of tax	0.0	(0.9)
Other comprehensive income (loss), net of tax	22.4	23.0
Accumulated other comprehensive income (loss), net of tax ending balance	13.9	48.1
Unfunded status of postretirement benefit plans
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance	(66.3)	(32.8)
Balance, January 1, 2018	(64.3)	(32.0)
Other comprehensive income (loss), before reclassifications, net of tax	2.0	0.8
Amounts reclassified from accumulated other comprehensive income, net of tax	0.0	0.0
Other comprehensive income (loss), net of tax	2.0	0.8
Accumulated other comprehensive income (loss), net of tax ending balance	(64.3)	(32.0)
Currency translation adjustments
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income (loss), net of tax beginning balance	(46.6)	(139.5)
Balance, January 1, 2018	(95.1)	(203.4)
Other comprehensive income (loss), before reclassifications, net of tax	(48.5)	(63.9)
Amounts reclassified from accumulated other comprehensive income, net of tax	0.0	0.0
Other comprehensive income (loss), net of tax	(48.5)	(63.9)
Accumulated other comprehensive income (loss), net of tax ending balance	$ (95.1)	$ (203.4)