Cash and Cash Equivalents and Restricted Cash and Cash Equivalents - PAC (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	$ 2,709	$ 1,290
Restricted cash and cash equivalents	216	140
Investments and restricted cash and cash equivalents and investments	17	15
Total cash and cash equivalents and restricted cash and cash equivalents	2,942	1,445	$ 2,096	$ 1,268
PAC
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	893	13
Restricted cash and cash equivalents	4	4
Investments and restricted cash and cash equivalents and investments	2	2
Total cash and cash equivalents and restricted cash and cash equivalents	$ 899	$ 19	$ 597	$ 36