Derivative Financial Instruments - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Dec. 31, 2020
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Potential recoveries	$ 0
Cash and securities pledged as collateral by counterparties	10,000,000
Securities pledged as collateral to counterparties	6,000,000
Collateral posted under MNAs for contracts containing credit-risk-contingent features	(4,000,000)	$ (13,000,000)
Cash and securities pledged in the form of margin deposits	54,000,000
Margin deposit liabilities	$ 12,000,000