Variable Interest Entities - Net Assets (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018
Variable Interest Entity [Line Items]
Noncontrolling interest	$ 132	$ 113
Great Valley Solar
Variable Interest Entity [Line Items]
Restricted cash	0	0
Non-utility property, less accumulated depreciation	311	313
Other assets	36	18
Total assets	347	331
Long-term debt due within one year	0	0
Other liabilities	33	17
Long-term debt	0	0
Total liabilities	33	17
Accumulated depreciation	3	1
Great Valley Solar | Tax Equity Investors
Variable Interest Entity [Line Items]
Noncontrolling interest	39	33
Copper Mountain - Mesquite Solar
Variable Interest Entity [Line Items]
Restricted cash	0	0
Non-utility property, less accumulated depreciation	492	492
Other assets	109	97
Total assets	601	589
Long-term debt due within one year	0	0
Other liabilities	45	33
Long-term debt	0	0
Total liabilities	45	33
Accumulated depreciation	4	1
Copper Mountain - Mesquite Solar | Tax Equity Investors
Variable Interest Entity [Line Items]
Noncontrolling interest	83	71
Texas Solar 4
Variable Interest Entity [Line Items]
Restricted cash	6	4
Non-utility property, less accumulated depreciation	95	98
Other assets	10	9
Total assets	111	111
Long-term debt due within one year	2	2
Other liabilities	28	26
Long-term debt	56	56
Total liabilities	86	84
Accumulated depreciation	$ 16	15
Texas Solar 4 | Third Party
Variable Interest Entity [Line Items]
Noncontrolling interest		$ 7	$ 7