Investments (Expected Sale of SoCore Energy) (Details) $ in Millions	3 Months Ended
	Mar. 31, 2018 USD ($)
Regulated Operations [Abstract]
Impairment charge	$ 66
Impairment charge, net of tax	48
Assets:
Cash and cash equivalents	18
Short-term restricted cash	25
Receivables	6
Non-utility property, plant and equipment1	203
Other assets	18
Total assets of business held for sale	270
Liabilities:
Accounts payable	1
Accrued liabilities	4
Debt obligations	82
Other liabilities	27
Noncontrolling interest (NCI)	28
Total liabilities and NCI of business held for sale	$ 142