Commitments and Contingencies, Leases (Details) (USD $)	12 Months Ended
	Dec. 31, 2013 Lease		Dec. 31, 2012	Dec. 31, 2011
Capital Leases [Abstract]
Number of leases qualifying as capital leases	3
Amortization expense under capital lease assets	$ 6,300,000		$ 5,700,000	$ 3,200,000
Property Held Under Capital Leases, Net [Abstract]
Property held under capital lease	221,200,000		221,200,000
Accumulated depreciation	(41,800,000)		(35,500,000)
Total property held under capital leases, net	179,400,000		185,700,000
Operating Leases, Future Minimum Payments Due [Abstract]
2014	109,600,000
2015	109,900,000
2016	95,700,000
2017	85,600,000
2018	85,900,000
Thereafter	596,600,000
Capital Leases, Future Minimum Payments Due [Abstract]
2014	30,600,000
2015	30,500,000
2016	29,300,000
2017	25,600,000
2018	25,200,000
Thereafter	538,200,000
Total minimum obligation	679,400,000
Interest component of obligation	(500,000,000)
Present value of minimum obligation	179,400,000
Purchased Power Agreements [Member]
Operating Leases [Abstract]
Payments for capacity for PPAs under operating lease obligations	79,600,000		59,400,000	47,900,000
Operating Leases, Future Minimum Payments Due [Abstract]
2014	94,800,000	[1],[2]
2015	95,300,000	[1],[2]
2016	84,000,000	[1],[2]
2017	78,700,000	[1],[2]
2018	79,300,000	[1],[2]
Thereafter	548,600,000	[1],[2]
WYCO Totem Gas Storage Facilities [Member]
Capital Leases [Abstract]
Ownership interest in joint venture (in hundredths)	50.00%
Capital lease obligations	144,200,000		148,700,000
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	96,600,000		77,900,000	71,300,000
Operating Leases, Future Minimum Payments Due [Abstract]
2014	14,800,000
2015	14,600,000
2016	11,700,000
2017	6,900,000
2018	6,600,000
Thereafter	$ 48,000,000

[1] PPA operating leases contractually expire through 2028.

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