Provision for Income Taxes (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
U.S. federal income taxes (including foreign withholding taxes):
Current federal income taxes									$ 92.2	$ 38.1	$ 154.1
Deferred federal income taxes									9.5	29.9	(37.6)
Total federal income taxes									101.7	68.0	116.5
State and local income taxes:
Current state and local income taxes									10.7	25.1	18.8
Deferred state and local income taxes									8.7	3.4	19.7
Total state and local income taxes									19.4	28.5	38.5
Foreign income taxes:
Current foreign income taxes									92.2	121.9	107.9
Deferred foreign income taxes									(8.5)	(19.2)	8.4
Total foreign income taxes									83.7	102.7	116.3
Provision for income taxes	$ 86.1	$ 64.6	$ 43.6	$ 10.5	$ 62.2	$ 60.7	$ 63.6	$ 12.7	$ 204.8	$ 199.2	$ 271.3