Summary of Changes in Goodwill Assets (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Goodwill [Line Items]
Cost, beginning balance	$ 3,648
Total Net, beginning balance	1,208
Goodwill from acquisitions	94
Cost, ending balance	3,742
Total Net, ending balance	1,302
Accumulated Impairment	(2,440)	$ (2,440)
Regulated Businesses
Goodwill [Line Items]
Cost, beginning balance	3,412
Goodwill from acquisitions	3
Cost, ending balance	3,415
Accumulated Impairment	(2,332)	(2,332)
Market-Based Businesses
Goodwill [Line Items]
Cost, beginning balance	236
Goodwill from acquisitions	91
Cost, ending balance	327
Accumulated Impairment	$ (108)	$ (108)