Investments (Securities Lending and Repurchase Agreements) (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 10,617	$ 12,092
Reinvestment portfolio - estimated fair value	10,241	11,833
Estimated fair value
Securities Financing Transaction [Line Items]
Securities loaned	10,377	11,756
Repurchase Agreements
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,975	3,125
Reinvestment portfolio - estimated fair value	2,898	3,057
Repurchase Agreements | Estimated fair value
Securities Financing Transaction [Line Items]
Securities Sold under Agreements to Repurchase	$ 3,030	$ 3,176