Non-Derivative Fair Value Measurements (Nonrecurring Fair Value Measurements) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Long-lived assets, carrying amount	$ 91,803	$ 82,010	$ 70,334
Impairment of long-lived assets		72
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	1,900
Fair value of long-lived assets	400
Impairment of long-lived assets	1,500
Impairment of long-lived assets, after tax	$ 1,200