Derivative Financial Instruments (Narrative) (Details) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2017 USD ($)	Jun. 30, 2016 USD ($)	Dec. 31, 2016 USD ($) subsidiary financing_facility
Derivative [Line Items]
Notional amount of derivative	$ 14,412.7		$ 14,412.7		$ 13,128.8
Aggregate actual adjusted qualifying borrowing base outstanding	459.2		459.2
Liability recorded based on Company's valuation	12.6		12.6		$ 11.3
Increase (decrease) of liability	0.4	$ (8.6)	1.3	$ (26.8)
TRS [Member]
Derivative [Line Items]
Number of derivative financing facilities | financing_facility					2
Number of wholly owned subsidiaries | subsidiary					2
Unutilized portion of facility accounted for as a derivative	625.0		625.0		$ 625.0
Notional amount of derivative	165.8		165.8		587.5
Canadian TRS [Member]
Derivative [Line Items]
Maximum aggregate facility commitment amounts	$ 1,062.3		$ 1,062.3		$ 474.8