Consolidated Statements of Operations - USD ($) shares in Millions, $ in Millions		12 Months Ended
		Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Operating revenues		$ 3,777	$ 3,610	$ 3,440
Operating expenses:
Operation and maintenance		1,622	1,544	1,479
Depreciation and amortization		604	582	545
General taxes		303	280	277
Loss (gain) on asset dispositions and purchases		0	34	(20)
Impairment charge		0	0	57
Total operating expenses, net		2,529	2,440	2,338
Operating income		1,248	1,170	1,102
Other income (expense):
Interest, net		(395)	(382)	(350)
Non-operating benefit costs, net		49	16	20
Other, net		22	29	15
Total other income (expense)		(324)	(337)	(315)
Income before income taxes		924	833	787
Provision for income taxes		215	212	222
Consolidated net income		709	621	565
Net loss attributable to noncontrolling interest		0	0	(2)
Net income attributable to common shareholders		$ 709	$ 621	$ 567
Basic earnings per share:
Net income attributable to common shareholders (USD per share)	[1]	$ 3.91	$ 3.44	$ 3.16
Diluted earnings per share:
Net income attributable to common shareholders (USD per share)	[1]	$ 3.91	$ 3.43	$ 3.15
Weighted average common shares outstanding:
Basic (in shares)		181	181	180
Diluted (in shares)		182	181	180

[1] Amounts may not calculate due to rounding.