Unaudited Quarterly Data - Schedule Of Unaudited Quarterly Data (Details) - USD ($) $ / shares in Units, $ in Millions |
3 Months Ended | 12 Months Ended | ||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Dec. 31, 2019 |
Sep. 30, 2019 |
Jun. 30, 2019 |
Mar. 31, 2019 |
Dec. 31, 2018 |
Sep. 30, 2018 |
Jun. 30, 2018 |
Mar. 31, 2018 |
Dec. 31, 2019 |
Dec. 31, 2018 |
Dec. 31, 2017 |
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| Quarterly Financial Data [Abstract] | ||||||||||||||||
| Operating revenues | $ 902 | $ 1,013 | $ 882 | $ 813 | $ 850 | $ 976 | $ 853 | $ 761 | $ 3,610 | $ 3,440 | $ 3,357 | |||||
| Operating income | 224 | 406 | 302 | 238 | 248 | 335 | 302 | 217 | 1,170 | 1,102 | 1,253 | |||||
| Net income attributable to common shareholders | $ 98 | $ 240 | $ 170 | $ 113 | $ 112 | $ 187 | $ 162 | $ 106 | $ 621 | $ 567 | $ 426 | |||||
| Basic earnings per share: | ||||||||||||||||
| Net income attributable to common shareholders (USD per share) | $ 0.54 | $ 1.33 | $ 0.94 | $ 0.62 | $ 0.62 | $ 1.04 | $ 0.90 | $ 0.60 | $ 3.44 | [1] | $ 3.16 | [1] | $ 2.39 | [1] | ||
| Diluted earnings per share: | ||||||||||||||||
| Net income attributable to common shareholders (USD per share) | $ 0.54 | $ 1.33 | $ 0.94 | $ 0.62 | $ 0.62 | $ 1.04 | $ 0.91 | $ 0.59 | $ 3.43 | [1] | $ 3.15 | [1] | $ 2.38 | [1] | ||
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