Provision for Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
U.S. federal income taxes (including foreign withholding taxes):
Current federal income taxes									$ 38.1	$ 154.1	$ 54.3
Deferred federal income taxes									29.9	(37.6)	35.7
Total federal income taxes									68.0	116.5	90.0
State and local income taxes:
Current state and local income taxes									25.1	18.8	8.2
Deferred state and local income taxes									3.4	19.7	(1.6)
Total state and local income taxes									28.5	38.5	6.6
Foreign income taxes:
Current foreign income taxes									121.9	107.9	89.8
Deferred foreign income taxes									(19.2)	8.4	10.5
Total foreign income taxes									102.7	116.3	100.3
Provision for income taxes	$ 62.2	$ 60.7	$ 63.6	$ 12.7	$ 135.1	$ 54.9	$ 81.6	$ (0.3)	$ 199.2	$ 271.3	$ 196.9