Investments (Securities Lending and Repurchase Agreements) (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 10,788	$ 12,092
Reinvestment portfolio — estimated fair value	10,553	11,833
Repurchase Agreements
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,975	3,125
Reinvestment portfolio — estimated fair value	2,913	3,057
Estimated fair value
Securities Financing Transaction [Line Items]
Securities loaned	10,510	11,756
Securities Sold under Agreements to Repurchase	$ 3,029	$ 3,176