Investments (Securities Lending and Repurchase Agreements Remaining Tenor) (Details) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 20,989	$ 18,628
Open (1)
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	6,196	2,949
1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	8,277	10,844
Over 1 Month to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	6,516	4,835
Maturity 180 to 360 Days [Member]
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	3,460	3,210
U.S. government and agency
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	19,845	17,508
U.S. government and agency | Open (1)
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	6,195	2,946
U.S. government and agency | 1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	7,955	10,553
U.S. government and agency | Over 1 Month to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	5,695	4,009
U.S. government and agency | Maturity 180 to 360 Days [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
U.S. government and agency | Repurchase Agreements
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	3,460	3,210
U.S. government and agency | Repurchase Agreements | Open (1)
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
U.S. government and agency | Repurchase Agreements | 1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	3,460	3,210
U.S. government and agency | Repurchase Agreements | Over 1 Month to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
U.S. government and agency | Repurchase Agreements | Maturity 180 to 360 Days [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Foreign government
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1,024	1,117
Foreign government | Open (1)
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
Foreign government | 1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	322	291
Foreign government | Over 1 Month to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	702	826
Foreign government | Maturity 180 to 360 Days [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
RMBS
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	119	0
RMBS | Open (1)
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
RMBS | 1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
RMBS | Over 1 Month to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	119	0
RMBS | Maturity 180 to 360 Days [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
U.S. corporate
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1	3
U.S. corporate | Open (1)
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	1	3
U.S. corporate | 1 Month or Less
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
U.S. corporate | Over 1 Month to 6 Months
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	0	0
U.S. corporate | Maturity 180 to 360 Days [Member]
Securities Financing Transaction [Line Items]
Cash collateral on deposit from counterparties	$ 0	$ 0