Income Taxes (Schedule of Composition of Income Tax Expense) (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Current:
Federal									$ 280.2	$ 169.6	$ 3,181.0
Foreign									299.8	106.8	47.5
State									(14.4)	4.7	(5.4)
Total current tax expense									565.6	281.1	3,223.1
Deferred:
Federal									141.3	(3.7)	(601.2)
Foreign									(24.1)	248.7	(230.9)
State									(54.8)	3.4	0.2
Total deferred tax (benefit) expense									62.4	248.4	(831.9)
Income taxes	$ 167.4	$ 151.9	$ 138.7	$ 170.0	$ (189.8)	$ 247.5	$ 273.3	$ 198.5	628.0	529.5	2,391.2
Current federal tax expense, utilization of net operating loss carryforward									$ 153.1
Current federal tax expense, effect of 2017 Tax Act										201.5	3,250.0
Deferred federal income tax benefit, effect of 2017 Tax Act										$ 26.2	$ 1,330.0