Commitments, Guarantees and Contingencies - Transmission (Details) - Jun. 30, 2015 $ in Millions	USD ($) Miles kV
CapX2020 [Member]
Transmission [Line Items]
Number of CapX2020 Projects	3
Capital Expenditures	$ 100
Great Northern Transmission Line [Member]
Transmission [Line Items]
Transmission Line Length (Miles) | Miles	220
Transmission Line Capacity (kV) | kV	500
Great Northern Transmission Line [Member] | Minimum [Member]
Transmission [Line Items]
Estimated Capital Expenditures	$ 560
Great Northern Transmission Line [Member] | Maximum [Member]
Transmission [Line Items]
Estimated Capital Expenditures	$ 710
Completed Projects - Current Year [Member] | CapX2020 [Member]
Transmission [Line Items]
Number of CapX2020 Projects	1
Completed Projects - Prior Years [Member] | CapX2020 [Member]
Transmission [Line Items]
Number of CapX2020 Projects	2