Accumulated Other Comprehensive Income (Components of Accumulated Other Comprehensive Income, Net of Tax) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Jan. 01, 2018
AOCI:
Beginning balance		$ 5,133.9	$ 4,281.5	$ 4,098.1
Change in accumulated other comprehensive income before reclassifications		578.2	(463.6)	156.0
Amounts reclassified from accumulated other comprehensive income		(11.3)	26.1	(16.6)
Total other comprehensive (loss) income		566.9	(437.5)	139.4
Cumulative adjustment to retained earnings	[1]				$ 7.5
Ending balance		5,682.1	5,133.9	4,281.5
Accumulated other comprehensive income (loss)
AOCI:
Beginning balance		(155.4)	234.0	94.6
Amounts reclassified from accumulated other comprehensive income		(11.3)	26.1	(16.6)
Total other comprehensive (loss) income		566.9	(437.5)	139.4
Cumulative adjustment to retained earnings			48.1		$ 48.1	[1]
Ending balance		411.5	(155.4)	234.0
Foreign currency translation adjustment
AOCI:
Beginning balance		(375.6)	(281.5)	(322.1)
Change in accumulated other comprehensive income before reclassifications		16.7	(94.2)	40.6
Amounts reclassified from accumulated other comprehensive income		0.0	0.0	0.0
Total other comprehensive (loss) income		16.7	(94.2)	40.6
Cumulative adjustment to retained earnings			0.1
Ending balance		(358.9)	(375.6)	(281.5)
Net unrealized gains on securities
AOCI:
Beginning balance		301.0	581.2	459.3
Change in accumulated other comprehensive income before reclassifications		564.6	(367.6)	140.2
Amounts reclassified from accumulated other comprehensive income		(9.1)	25.3	(18.3)
Total other comprehensive (loss) income		555.5	(342.3)	121.9
Cumulative adjustment to retained earnings			62.1
Ending balance		856.5	301.0	581.2
Net unrealized gains on derivative transactions
AOCI:
Beginning balance		18.4	0.0
Change in accumulated other comprehensive income before reclassifications		1.0	20.1
Amounts reclassified from accumulated other comprehensive income		(2.3)	(1.7)
Total other comprehensive (loss) income		(1.3)	18.4
Cumulative adjustment to retained earnings			0.0
Ending balance		17.1	18.4	0.0
OTTI
AOCI:
Beginning balance		15.1	17.9	20.6
Change in accumulated other comprehensive income before reclassifications		0.4	(6.7)	(2.7)
Amounts reclassified from accumulated other comprehensive income		0.0	0.0	0.0
Total other comprehensive (loss) income		0.4	(6.7)	(2.7)
Cumulative adjustment to retained earnings			3.9
Ending balance		15.5	15.1	17.9
Unamortized net (losses) on Pension Plans
AOCI:
Beginning balance		(114.3)	(83.6)	(63.2)
Change in accumulated other comprehensive income before reclassifications		(4.5)	(15.2)	(22.1)
Amounts reclassified from accumulated other comprehensive income		0.1	2.5	1.7
Total other comprehensive (loss) income		(4.4)	(12.7)	(20.4)
Cumulative adjustment to retained earnings			(18.0)
Ending balance		$ (118.7)	$ (114.3)	$ (83.6)

[1] Amounts relate to: (i) the requirement to recognize the changes in fair value of equity securities directly within income (resulting in a reclassification of unrealized gains as of December 31, 2017 between accumulated other comprehensive income (“AOCI”) and retained earnings); (ii) the impact of adoption of the new revenue recognition standard for revenues from service contracts and sales of products; and (iii) the reclassification from AOCI to retained earnings for stranded tax effects resulting from the U.S. Tax Cuts and Jobs Act. See Note 2 for additional information.