Accumulated Other Comprehensive Income (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Balance at December 31, 2015			$ 20,551.8	$ 20,923.5
Other comprehensive income (loss), net of tax	$ (90.4)	$ (99.7)	103.7	(100.8)
Balance at September 30, 2016	21,264.9	21,376.8	21,264.9	21,376.8
Accumulated Other Comprehensive Income (Loss) [Member]
Balance at December 31, 2015			(80.8)	6.2
Comprehensive Income Before Reclassification Adjustments			175.2	(106.0)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax			(4.8)	(0.5)
Other Comprehensive Income (Loss), Net of Tax			(66.7)	5.7
Other comprehensive income (loss), net of tax			103.7	(100.8)
Balance at September 30, 2016	22.9	(94.6)	22.9	(94.6)
Foreign Currency Translation [Member]
Balance at December 31, 2015			(8.8)	(2.2)
Comprehensive Income Before Reclassification Adjustments			(5.6)	(10.0)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax			0.0	0.0
Other Comprehensive Income (Loss), Net of Tax			1.0	3.6
Other comprehensive income (loss), net of tax			(4.6)	(6.4)
Balance at September 30, 2016	(13.4)	(8.6)	(13.4)	(8.6)
Derivative Investments [Member]
Balance at December 31, 2015			59.6	62.6
Comprehensive Income Before Reclassification Adjustments			0.0	(4.7)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax			(0.9)	0.9
Other Comprehensive Income (Loss), Net of Tax			0.3	1.5
Other comprehensive income (loss), net of tax			(0.6)	(2.3)
Balance at September 30, 2016	59.0	60.3	59.0	60.3
Defined Benefit Plans [Member]
Balance at December 31, 2015			(36.6)	(31.3)
Comprehensive Income Before Reclassification Adjustments			3.1	(0.3)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax			2.4	2.0
Other Comprehensive Income (Loss), Net of Tax			(2.1)	(0.6)
Other comprehensive income (loss), net of tax			3.4	1.1
Balance at September 30, 2016	(33.2)	(30.2)	(33.2)	(30.2)
Investment Securities [Member]
Balance at December 31, 2015			(95.0)	(22.9)
Comprehensive Income Before Reclassification Adjustments			177.7	(91.0)
Reclassification from Accumulated Other Comprehensive Income, Current Period, before Tax			(6.3)	(3.4)
Other Comprehensive Income (Loss), Net of Tax			(65.9)	1.2
Other comprehensive income (loss), net of tax			105.5	(93.2)
Balance at September 30, 2016	$ 10.5	$ (116.1)	$ 10.5	$ (116.1)