Accumulated Other Comprehensive Income (Loss) (Components of AOCI) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at the beginning of the period			$ 914.8	$ 94.0
Other comprehensive income (loss) before reclassifications			(32.0)	452.2
Amounts reclassified from accumulated other comprehensive income			(243.6)	6.3
Total other comprehensive income (loss)	$ (418.9)	$ 388.8	(275.6)	458.5
Balance at the end of the period	639.2	552.5	639.2	552.5
Pension Liability
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at the beginning of the period			(15.5)	(6.9)
Other comprehensive income (loss) before reclassifications			(7.6)	0.0
Amounts reclassified from accumulated other comprehensive income			0.0	0.0
Total other comprehensive income (loss)			(7.6)	0.0
Balance at the end of the period	(23.1)	(6.9)	(23.1)	(6.9)
Net Unrealized Gains (Losses) From Marketable Securities
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at the beginning of the period			460.9	137.3
Other comprehensive income (loss) before reclassifications			(297.8)	129.6
Amounts reclassified from accumulated other comprehensive income			7.5	2.7
Total other comprehensive income (loss)			(290.3)	132.3
Balance at the end of the period	170.6	269.6	170.6	269.6
Net Unrealized Gains (Losses) From Hedges
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at the beginning of the period			519.6	(36.0)
Other comprehensive income (loss) before reclassifications			285.3	355.1
Amounts reclassified from accumulated other comprehensive income			(251.1)	3.6
Total other comprehensive income (loss)			34.2	358.7
Balance at the end of the period	553.8	322.7	553.8	322.7
Foreign Currency Translation Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Balance at the beginning of the period			(50.2)	(0.4)
Other comprehensive income (loss) before reclassifications			(11.9)	(32.5)
Amounts reclassified from accumulated other comprehensive income			0.0	0.0
Total other comprehensive income (loss)			(11.9)	(32.5)
Balance at the end of the period	$ (62.1)	$ (32.9)	$ (62.1)	$ (32.9)