Variable Interest Entities - Net Assets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Variable Interest Entity [Line Items]
Noncontrolling interest	$ 175	$ 113
Great Valley Solar
Variable Interest Entity [Line Items]
Restricted cash	0	0
Non-utility property, less accumulated depreciation	295	313
Other assets	47	18
Total assets	342	331
Long-term debt due within one year	0	0
Other liabilities	19	17
Long-term debt	0	0
Total liabilities	19	17
Accumulated depreciation	7	1
Great Valley Solar | Tax Equity Investors
Variable Interest Entity [Line Items]
Noncontrolling interest	57	33
Copper Mountain - Mesquite Solar
Variable Interest Entity [Line Items]
Restricted cash	0	0
Non-utility property, less accumulated depreciation	465	492
Other assets	131	97
Total assets	596	589
Long-term debt due within one year	0	0
Other liabilities	22	33
Long-term debt	0	0
Total liabilities	22	33
Accumulated depreciation	10	1
Copper Mountain - Mesquite Solar | Tax Equity Investors
Variable Interest Entity [Line Items]
Noncontrolling interest	$ 115	71
Texas Solar 4
Variable Interest Entity [Line Items]
Restricted cash		4
Non-utility property, less accumulated depreciation		98
Other assets		9
Total assets		111
Long-term debt due within one year		2
Other liabilities		26
Long-term debt		56
Total liabilities		84
Accumulated depreciation		15
Texas Solar 4 | Third Party
Variable Interest Entity [Line Items]
Noncontrolling interest		$ 7