Background - Recently Adopted Accounting Pronouncements (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2019	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Member's equity	$ (13,197)	$ (12,738)	$ (13,197)	$ (12,738)			$ (12,905)
Income tax expense (benefit)	37	42	150	147
MEMBER'S EQUITY
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Member's equity	$ (13,532)	$ (13,096)	$ (13,532)	$ (13,096)	$ (13,724)	$ (13,412)	$ (13,139)	$ (13,301)
MEMBER'S EQUITY | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Member's equity					3
Income tax expense (benefit)					$ (2)