Commitments and Contingencies, Leases (Details) (USD $)	12 Months Ended
	Dec. 31, 2014 Lease		Dec. 31, 2013	Dec. 31, 2012
Capital Leases [Abstract]
Number of leases qualifying as capital leases	3
Amortization expense under capital lease assets	$ 7,200,000		$ 6,300,000	$ 5,700,000
Property Held Under Capital Leases, Net [Abstract]
Property held under capital lease	221,200,000		221,200,000
Accumulated depreciation	(49,000,000)		(41,800,000)
Total property held under capital leases, net	172,200,000		179,400,000
Operating Leases, Future Minimum Payments Due [Abstract]
2015	128,300,000
2016	114,500,000
2017	103,500,000
2018	103,400,000
2019	104,200,000
Thereafter	729,800,000
Capital Leases, Future Minimum Payments Due [Abstract]
2015	30,500,000
2016	29,300,000
2017	25,600,000
2018	25,300,000
2019	25,100,000
Thereafter	511,500,000
Total minimum obligation	647,300,000
Interest component of obligation	(475,100,000)
Present value of minimum obligation	172,200,000
Maximum [Member]
Operating Leased Assets [Line Items]
Purchase Power Agreement Duration, Maximum	2032
Purchased Power Agreements [Member]
Operating Leases [Abstract]
Payments for capacity for PPAs under operating lease obligations	110,100,000		79,600,000	59,400,000
Operating Leases, Future Minimum Payments Due [Abstract]
2015	113,800,000	[1],[2]
2016	102,800,000	[1],[2]
2017	96,500,000	[1],[2]
2018	96,700,000	[1],[2]
2019	97,600,000	[1],[2]
Thereafter	688,000,000	[1],[2]
WYCO Totem Gas Storage Facilities [Member]
Capital Leases [Abstract]
Ownership interest in joint venture (in hundredths)	50.00%
Capital lease obligations	138,900,000		144,200,000
Storage, Leaseholds and Rights [Member]
Property Held Under Capital Leases, Net [Abstract]
Property held under capital lease	200,500,000		200,500,000
Gas Pipeline [Member]
Property Held Under Capital Leases, Net [Abstract]
Property held under capital lease	20,700,000		20,700,000
Other [Member]
Operating Leases [Abstract]
Total expenses under operating lease obligations	126,200,000		96,600,000	77,900,000
Operating Leases, Future Minimum Payments Due [Abstract]
2015	14,500,000
2016	11,700,000
2017	7,000,000
2018	6,700,000
2019	6,600,000
Thereafter	$ 41,800,000

[1] PPA operating leases contractually expire through 2032.

[2] Amounts do not include PPAs accounted for as executory contracts.