Income Taxes - Income Tax (Benefit) Expense Attributable to Income from Continuing Operations (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Current:
Current Income Tax Expense (Benefit)	$ 608.8	$ 163.8	$ 194.5
Deferred:
Total	(742.4)	80.1	(32.3)
Income tax (benefit) expense	(133.6)	243.9	162.2
Canada
Current:
Foreign	438.1	78.6	107.2
Deferred:
Foreign	(301.8)	49.0	(48.1)
United States
Current:
U.S. Federal	113.2	45.4	46.1
U.S. state, net of federal income tax benefit	3.0	1.5	4.1
Deferred:
U.S. Federal	(473.3)	37.0	21.0
U.S. state, net of federal income tax benefit	34.3	(6.9)	(7.5)
Other Foreign
Current:
Foreign	54.5	38.3	37.1
Deferred:
Foreign	$ (1.6)	$ 1.0	$ 2.3