Cash and Cash Equivalents and Restricted Cash and Cash Equivalents - MEC (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
Total cash and cash equivalents and restricted cash and cash equivalents	2,942	1,445	$ 2,096	$ 1,268
MEC
Condensed Cash Flow Statements, Captions [Line Items]
Cash and cash equivalents	541	38
Restricted cash and cash equivalents	7	7
Total cash and cash equivalents and restricted cash and cash equivalents	$ 548	$ 45	$ 199	$ 330