Commitments, Guarantees and Contingencies - Transmission (Details) $ in Millions	Dec. 31, 2015 USD ($) Miles kV
CapX2020 [Member]
Transmission [Line Items]
Number of Projects	3
Total Project Costs	$ 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]
Total Project Cost	$ 560
Great Northern Transmission Line [Member] | Maximum [Member]
Transmission [Line Items]
Total Project Cost	$ 710
Completed Project - Prior Years [Member] | CapX2020 [Member]
Transmission [Line Items]
Number of Projects	2