Derivatives - Offsetting Assets (Details) $ in Millions	6 Months Ended
	Jun. 30, 2021 USD ($) Counterparty	Dec. 31, 2020 USD ($)
Offsetting of Financial Assets under Master Netting Agreements with Derivative Counterparties
Number of master netting agreements supported by primary counterparty's parent guarantee | Counterparty	17
Number of credit support agreements by primary counterparty | Counterparty	16
Gross Amounts of Derivative Assets Presented in the Consolidated Balance Sheet	$ 75	$ 44
Net Amount of Derivative Assets	44	33
Derivatives subject to master netting agreements
Offsetting of Financial Assets under Master Netting Agreements with Derivative Counterparties
Gross Amounts of Derivative Assets Presented in the Consolidated Balance Sheet	74	44
Gross Amount of Eligible Offsetting Recognized Derivative Liabilities	31	11
Net Amount of Derivative Assets	43	$ 33
Derivatives not subject to master netting agreements
Offsetting of Financial Assets under Master Netting Agreements with Derivative Counterparties
Gross Amounts of Derivative Assets Presented in the Consolidated Balance Sheet	1
Net Amount of Derivative Assets	$ 1