Investments (Securities Lending and Repurchase Agreements Remaining Tenor) (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 11,089	$ 10,788
U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	9,907	9,418
Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1,009	1,107
Agency RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	173	263
Open (1)
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1,772	1,393
Open (1) | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1,772	1,393
Open (1) | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Open (1) | Agency RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	5,640	4,677
1 Month or Less | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	4,687	4,106
1 Month or Less | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	856	483
1 Month or Less | Agency RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	97	88
Over 1 Month to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	3,677	4,718
Over 1 Month to 6 Months | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	3,448	3,919
Over 1 Month to 6 Months | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	153	624
Over 1 Month to 6 Months | Agency RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	76	175
Over 6 Months to 1 Year
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Over 6 Months to 1 Year | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Over 6 Months to 1 Year | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Over 6 Months to 1 Year | Agency RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Repurchase Agreements
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,975	2,975
Repurchase Agreements | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,975	2,975
Repurchase Agreements | Open (1) | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Repurchase Agreements | 1 Month or Less | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,975	2,975
Repurchase Agreements | Over 1 Month to 6 Months | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Repurchase Agreements | Over 6 Months to 1 Year | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 0	$ 0