Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018	Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	$ 37.3	$ (814.2)	$ 127.5		$ (51.0)
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	865.5	(910.6)	205.6
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	14.0	13.6	27.1
Total Other Comprehensive Income (Loss)	851.5	(924.2)	178.5
Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect of New Accounting Principle in Period of Adoption				$ (17.5)
Net Unrealized Gain (Loss) on Securities
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	615.9	(312.4)	607.8		440.6
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	894.1	(920.3)	176.7
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(34.2)	(17.6)	9.5
Total Other Comprehensive Income (Loss)	928.3	(902.7)	167.2
Net Unrealized Gain (Loss) on Securities | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect of New Accounting Principle in Period of Adoption				(17.5)
Net Gain on Hedges
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	187.8	250.6	282.3		327.5
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(0.2)	16.8	(14.7)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	62.6	48.5	30.5
Total Other Comprehensive Income (Loss)	(62.8)	(31.7)	(45.2)
Net Gain on Hedges | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect of New Accounting Principle in Period of Adoption				0.0
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(281.6)	(305.2)	(254.5)		(354.0)
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	23.6	(50.7)	99.5
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	0.0	0.0	0.0
Total Other Comprehensive Income (Loss)	23.6	(50.7)	99.5
Foreign Currency Translation Adjustment | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect of New Accounting Principle in Period of Adoption				0.0
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income (Loss)
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest	(484.8)	(447.2)	(508.1)		$ (465.1)
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(52.0)	43.6	(55.9)
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax	(14.4)	(17.3)	(12.9)
Total Other Comprehensive Income (Loss)	$ (37.6)	$ 60.9	$ (43.0)
Unrecognized Pension and Postretirement Benefit Costs | Accounting Standards Update 2016-01
Accumulated Other Comprehensive Income (Loss)
Cumulative Effect of New Accounting Principle in Period of Adoption				$ 0.0