Schedule of Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Accumulated Other Comprehensive Income, Net of Tax
Net Other Comprehensive Income (Loss)	$ (192.4)	$ 51.4
Balance at End of Period	9,499.5	9,107.4
Net Unrealized Gain on Securities
Accumulated Other Comprehensive Income, Net of Tax
Balance at Beginning of Period	607.8	440.6
Balance at Beginning of Period, as Adjusted	590.3
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(234.8)	44.7
Reclassification from Accumulated Other Comprehensive Income or Loss	0.6	(2.3)
Net Other Comprehensive Income (Loss)	(234.2)	42.4
Balance at End of Period	356.1	483.0
Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Accumulated Other Comprehensive Income, Net of Tax
Balance at Beginning of Period	282.3	327.5
Balance at Beginning of Period, as Adjusted	282.3
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	2.9	(2.7)
Reclassification from Accumulated Other Comprehensive Income or Loss	(11.7)	(8.0)
Net Other Comprehensive Income (Loss)	(8.8)	(10.7)
Balance at End of Period	273.5	316.8
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income, Net of Tax
Balance at Beginning of Period	(254.5)	(354.0)
Balance at Beginning of Period, as Adjusted	(254.5)
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	47.5	17.1
Reclassification from Accumulated Other Comprehensive Income or Loss	0.0	0.0
Net Other Comprehensive Income (Loss)	47.5	17.1
Balance at End of Period	(207.0)	(336.9)
Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income, Net of Tax
Balance at Beginning of Period	(508.1)	(465.1)
Balance at Beginning of Period, as Adjusted	(508.1)
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(1.2)	(0.6)
Reclassification from Accumulated Other Comprehensive Income or Loss	4.3	3.2
Net Other Comprehensive Income (Loss)	3.1	2.6
Balance at End of Period	(505.0)	(462.5)
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income, Net of Tax
Balance at Beginning of Period	127.5	(51.0)
Cumulative Effect of New Accounting Principle in Period of Adoption	(17.5)	0.0
Balance at Beginning of Period, as Adjusted	110.0	(51.0)
Other Comprehensive Income (Loss) Before Reclassifications, Net of Tax	(185.6)	58.5
Reclassification from Accumulated Other Comprehensive Income or Loss	(6.8)	(7.1)
Net Other Comprehensive Income (Loss)	(192.4)	51.4
Balance at End of Period	(82.4)	$ 0.4
Restatement Adjustment | Accounting Standards Update 2016-01 | Net Unrealized Gain on Securities
Accumulated Other Comprehensive Income, Net of Tax
Cumulative Effect of New Accounting Principle in Period of Adoption	(17.5)
Restatement Adjustment | Accounting Standards Update 2016-01 | Accumulated Net Gain (Loss) from Designated or Qualifying Hedges
Accumulated Other Comprehensive Income, Net of Tax
Cumulative Effect of New Accounting Principle in Period of Adoption	0.0
Restatement Adjustment | Accounting Standards Update 2016-01 | Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income, Net of Tax
Cumulative Effect of New Accounting Principle in Period of Adoption	0.0
Restatement Adjustment | Accounting Standards Update 2016-01 | Unrecognized Pension and Postretirement Benefit Costs
Accumulated Other Comprehensive Income, Net of Tax
Cumulative Effect of New Accounting Principle in Period of Adoption	0.0
Restatement Adjustment | Accounting Standards Update 2016-01 | Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income, Net of Tax
Cumulative Effect of New Accounting Principle in Period of Adoption	$ (17.5)