Supplemental Cash Flow Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Related Party Transaction [Line Items]
Cash (paid) for interest, net of amount capitalized	$ (411.9)	$ (329.6)	$ (241.4)
Cash received for income taxes, net	39.7
Cash (paid) for income taxes, net		(9.3)	(22.0)
Accounts payable related to construction costs	170.1	177.1	1.8
Restricted cash used to purchase investments held in the rabbi trust	59.2	60.2	0.0
Restricted cash	33.6	118.4
Amortization of deferred revenue	24.7	39.9	55.7
AMP Trillium LLC [Member]
Related Party Transaction [Line Items]
Note reveivable received related to the sale of AMP Trillium	0.0	12.0	0.0
Capital assets received related to the sale of AMP Trillium	$ 0.0	$ 6.3	$ 0.0
Equity method investment, ownership interest (as a percent)		30.00%