Derivatives - Offsetting Assets (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($) Counterparty	Dec. 31, 2019 USD ($)
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	$ 44	$ 142
Net Amount of Derivative Assets	33	128
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	44	142
Gross Amount of Eligible Offsetting Recognized Derivative Liabilities	11	14
Net Amount of Derivative Assets	$ 33	$ 128