Investments (Securities Lending, Repurchase Agreements and FHLB Agreements Remaining Tenor) (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 17,369	$ 18,005
U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	16,267	16,951
Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1,026	975
RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	76	79
Municipals
Securities Financing Transaction [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	800	800
Open
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,928	2,736
Open | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,928	2,736
Open | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Open | RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Open | Municipals
Securities Financing Transaction [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	0	0
1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	7,011	9,288
1 Month or Less | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	6,676	8,995
1 Month or Less | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	259	214
1 Month or Less | RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	76	79
1 Month or Less | Municipals
Securities Financing Transaction [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	250	150
Over 1 to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	7,430	5,981
Over 1 to 6 Months | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	6,663	5,220
Over 1 to 6 Months | Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	767	761
Over 1 to 6 Months | RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Over 1 to 6 Months | Municipals
Securities Financing Transaction [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	475	650
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 | RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Over 6 Months to 1 Year | Municipals
Securities Financing Transaction [Line Items]
Federal Home Loan Bank, Advances, Branch of FHLB Bank, Amount of Advances	75	0
Repurchase Agreements
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,310	1,067
Repurchase Agreements | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,310	1,000
Repurchase Agreements | All other corporate and government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	67
Repurchase Agreements | Open
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Repurchase Agreements | Open | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Repurchase Agreements | Open | All other corporate and government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Repurchase Agreements | 1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,310	1,000
Repurchase Agreements | 1 Month or Less | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	2,310	1,000
Repurchase Agreements | 1 Month or Less | All other corporate and government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Repurchase Agreements | Over 1 to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	67
Repurchase Agreements | Over 1 to 6 Months | U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Repurchase Agreements | Over 1 to 6 Months | All other corporate and government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	67
Repurchase Agreements | Over 6 Months to 1 Year
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
Repurchase Agreements | Over 6 Months to 1 Year | All other corporate and government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 0	$ 0