Unaudited Quarterly Data - Schedule Of Unaudited Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2021	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2021		Dec. 31, 2020		Dec. 31, 2019
Quarterly Financial Data [Abstract]
Operating revenues	$ 951	$ 1,092	$ 999	$ 888	$ 923	$ 1,079	$ 931	$ 844	$ 3,930		$ 3,777		$ 3,610
Operating income	220	417	330	229	263	433	313	239	1,196		1,248		1,214
Net income attributable to common shareholders	$ 645	$ 278	$ 207	$ 133	$ 145	$ 264	$ 176	$ 124	$ 1,263		$ 709		$ 621
Basic earnings per share:
Net income attributable to common shareholders (USD per share)	$ 3.55	$ 1.53	$ 1.14	$ 0.73	$ 0.80	$ 1.46	$ 0.97	$ 0.69	$ 6.96	[1]	$ 3.91	[1]	$ 3.44	[1]
Diluted earnings per share:
Net income attributable to common shareholders (USD per share)	$ 3.55	$ 1.53	$ 1.14	$ 0.73	$ 0.80	$ 1.46	$ 0.97	$ 0.68	$ 6.95	[1]	$ 3.91	[1]	$ 3.43	[1]

[1] Amounts may not calculate due to rounding.