Condensed Parent Company Financial Statements (Condensed Balance Sheets) (Details) - USD ($) $ in Millions	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Current assets:
Other	$ 123	$ 144
Total current assets	887	876
Investments:
Other	154	148
Total investments	485	468
Other assets	2,002	1,830
Total assets	17,710	16,701	$ 15,426
Current liabilities:
Commercial paper	389	337
Other	207	356
Total current liabilities	1,297	2,054
Other liabilities	374	299
Common Equity:
Retained earnings	2,994	2,766
Accumulated other comprehensive income (loss)	(1)	1
Shares in deferred compensation trust	(11)	(10)
Total common equity	5,688	5,205
Total liabilities and equity	17,710	16,701
Parent Company [Member]
Current assets:
Notes receivable from affiliated companies	32	27
Other	5	6
Total current assets	37	33
Investments:
Investments in consolidated subsidiaries	6,664	6,017
Other	2	1
Total investments	6,666	6,018
Other assets	88	89
Total assets	6,791	6,140
Current liabilities:
Commercial paper	132	169
Notes payable to affiliated companies	937	731
Other	29	19
Total current liabilities	1,098	919
Other liabilities	2	15
Common Equity:
Common stock and additional paid-in capital	2,706	2,448
Retained earnings	2,996	2,766
Accumulated other comprehensive income (loss)	0	2
Shares in deferred compensation trust	(11)	(10)
Total common equity	5,691	5,206
Total liabilities and equity	$ 6,791	$ 6,140