Commitments and Contingencies - Narrative (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2023	Dec. 31, 2022
Loss Contingencies [Line Items]
Pledged Collateral	$ 1,074	$ 997
Securities pledged as collateral
Loss Contingencies [Line Items]
Securities Pledged under repurchase agreements	122	102
Acquisition of mortgage loans
Loss Contingencies [Line Items]
Amount of purchase commitment	65
Purchase of limited partnerships and private placement investments
Loss Contingencies [Line Items]
Amount of purchase commitment	655
Federal Home Loan Bank of Boston | Line of Credit
Loss Contingencies [Line Items]
Non-putable funding agreements issued to FHLB	811	730
Pledged Collateral	$ 1,074	$ 997