Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 374.2	$ 37.3	$ (814.2)		$ 127.5
Other Comprehensive Income (Loss) Before Reclassifications	359.4	865.5	(910.6)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	22.5	14.0	13.6
Total Other Comprehensive Income (Loss)	336.9	851.5	(924.2)
Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect, Period of Adoption, Adjustment				$ (17.5)
Net Unrealized Gain (Loss) on Securities
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	1,067.7	615.9	(312.4)		607.8
Other Comprehensive Income (Loss) Before Reclassifications	405.6	894.1	(920.3)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(46.2)	(34.2)	(17.6)
Total Other Comprehensive Income (Loss)	451.8	928.3	(902.7)
Net Unrealized Gain (Loss) on Securities | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect, Period of Adoption, Adjustment				(17.5)
Net Gain on Hedges
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	97.8	187.8	250.6		282.3
Other Comprehensive Income (Loss) Before Reclassifications	(5.7)	(0.2)	16.8
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	84.3	62.6	48.5
Total Other Comprehensive Income (Loss)	(90.0)	(62.8)	(31.7)
Net Gain on Hedges | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect, Period of Adoption, Adjustment				0.0
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(261.3)	(281.6)	(305.2)		(254.5)
Other Comprehensive Income (Loss) Before Reclassifications	20.3	23.6	(50.7)
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	0.0	0.0	0.0
Total Other Comprehensive Income (Loss)	20.3	23.6	(50.7)
Foreign Currency Translation Adjustment | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect, Period of Adoption, Adjustment				0.0
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(530.0)	(484.8)	(447.2)		$ (508.1)
Other Comprehensive Income (Loss) Before Reclassifications	(60.8)	(52.0)	43.6
Amounts Reclassified from Accumulated Other Comprehensive Income or Loss	(15.6)	(14.4)	(17.3)
Total Other Comprehensive Income (Loss)	$ (45.2)	$ (37.6)	$ 60.9
Unrecognized Pension and Postretirement Benefit Costs | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect, Period of Adoption, Adjustment				$ 0.0