Variable Interest Entities - Net Assets (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Noncontrolling interest	$ 156	$ 113
Great Valley Solar
Variable Interest Entity [Line Items]
Restricted cash	0	0
Non-utility property, less accumulated depreciation	309	313
Other assets	39	18
Total assets	348	331
Long-term debt due within one year	0	0
Other liabilities	32	17
Long-term debt	0	0
Total liabilities	32	17
Accumulated depreciation	5	1
Great Valley Solar | Tax Equity Investors
Variable Interest Entity [Line Items]
Noncontrolling interest	48	33
Copper Mountain - Mesquite Solar
Variable Interest Entity [Line Items]
Restricted cash	0	0
Non-utility property, less accumulated depreciation	488	492
Other assets	109	97
Total assets	597	589
Long-term debt due within one year	0	0
Other liabilities	43	33
Long-term debt	0	0
Total liabilities	43	33
Accumulated depreciation	8	1
Copper Mountain - Mesquite Solar | Tax Equity Investors
Variable Interest Entity [Line Items]
Noncontrolling interest	99	71
Texas Solar 4
Variable Interest Entity [Line Items]
Restricted cash	7	4
Non-utility property, less accumulated depreciation	96	98
Other assets	10	9
Total assets	113	111
Long-term debt due within one year	57	2
Other liabilities	28	26
Long-term debt	0	56
Total liabilities	85	84
Accumulated depreciation	$ 17	15
Texas Solar 4 | Third Party
Variable Interest Entity [Line Items]
Noncontrolling interest		$ 7