Fair Value Measurements (Nonrecurring Fair Value Measurements) (Details) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Jan. 31, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets, carrying amount		$ 82,010	$ 70,334
Impairment of long-lived assets		72	$ 11	$ 446
Impairment of long-lived assets, after tax		$ 54
NEER [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets, carrying amount				502
Fair value of long-lived assets				82
Impairment of long-lived assets				420
Impairment of long-lived assets, after tax				$ 258
Jointly Owned Nuclear Power Plant 2 Member | NEER [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Proportionate ownership share		70.00%	70.00%
Purchased Power Agreements [Member] | NEER [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Shortened term	5 years