Goodwill and Other Intangible Assets, Goodwill (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Goodwill [Roll Forward]
Goodwill, beginning balance	$ 767	$ 665
Acquisitions	18	100
Other adjustments		2
Goodwill, ending balance	785	767
CNA Financial [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	112	110
Other adjustments		2
Goodwill, ending balance	112	112
Boardwalk Pipelines [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	237	237
Goodwill, ending balance	237	237
Corporate [Member]
Goodwill [Roll Forward]
Goodwill, beginning balance	418	318
Acquisitions	18	100
Goodwill, ending balance	$ 436	$ 418