Commitments, Guarantees and Contingencies - Transmission (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
CapX2020 [Member]
Transmission [Line Items]
Number of CapX2020 Projects	3
Capital Cost Spent to Date	$ 85.7
CapX2020 [Member] | Minimum [Member]
Transmission [Line Items]
Estimated Capital Expenditures	100
CapX2020 [Member] | Maximum [Member]
Transmission [Line Items]
Estimated Capital Expenditures	110
Great Northern Transmission Line [Member]
Transmission [Line Items]
Transmission Line Length (Miles)	220
Transmission Line Capacity (kV)	500
Great Northern Transmission Line [Member] | Minimum [Member]
Transmission [Line Items]
Estimated Capital Expenditures	500
Great Northern Transmission Line [Member] | Maximum [Member]
Transmission [Line Items]
Estimated Capital Expenditures	$ 650
Project in Progress [Member] | CapX2020 [Member]
Transmission [Line Items]
Number of CapX2020 Projects	1
Completed Project [Member] [Member] | CapX2020 [Member]
Transmission [Line Items]
Number of CapX2020 Projects	2