Shareholders' Deficit (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021		Sep. 30, 2020	Jun. 30, 2021
Repurchase Of Shares Of Common Stock [Line Items]
Repurchase of shares of Common Stock, value	$ 330	$ 0	$ 860		$ 0
Value of share repurchases with trade dates during the current reporting date but with settlement dates subsequent to the current reporting date			$ 14
Number of shares repurchased with trade dates during the current reporting date but with settlement dates subsequent to the current reporting date			100,000
Value of shares repurchased with trade dates prior to the current reporting quarter, but settlement dates in the current quarter			$ 11
Number of shares repurchased with trade dates prior to the current reporting quarter, but settlement dates in the current quarter			100,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	1,670		$ 1,670
May 2021
Repurchase Of Shares Of Common Stock [Line Items]
Repurchase of shares of Common Stock, value			330		0
Stock Repurchase Program, Authorized Amount	2,000		2,000
Stock Repurchase Program, Remaining Authorized Repurchase Amount	1,670		1,670
November 2019
Repurchase Of Shares Of Common Stock [Line Items]
Repurchase of shares of Common Stock, value			530	[1]	$ 0
Stock Repurchase Program, Remaining Authorized Repurchase Amount	$ 0		$ 0			$ 1,200
Issued Common Stock
Repurchase Of Shares Of Common Stock [Line Items]
Shares Repurchased	2,000,000		7,348,000		0
Repurchase of shares of Common Stock, value	$ 0		$ 24
Issued Common Stock | May 2021
Repurchase Of Shares Of Common Stock [Line Items]
Shares Repurchased			2,602,000		0
Issued Common Stock | November 2019
Repurchase Of Shares Of Common Stock [Line Items]
Shares Repurchased			4,746,000	[1]	0

[1] (a)    Includes the effect of $14 million in share repurchases (0.1 million shares) with trade dates on, or prior to, September 30, 2021, but cash settlement dates subsequent to September 30, 2021 and excludes the effect of $11 million in share repurchases (0.1 million shares) with trade dates on, or prior to, December 31, 2020, but cash settlement dates subsequent to December 31, 2020.