Investments (Fair Value and Losses by Investment Category and Length of Time in a Loss Position) (Details) - Fixed maturities - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	$ 21,898	$ 79,899
Less Than Twelve Months, Gross Unrealized Loss	437	3,108
Twelve Months or More, Fair Value	15,006	46,570
Twelve Months or More, Gross Unrealized Losses	878	3,283
Total, Fair Value	36,904	126,469
Total, Gross Unrealized Losses	1,315	6,391
Fair Value not reflected in AOCI, held-to-maturity securities	0	13
Gross Unrealized Losses not reflected in AOCI, held-to-maturity securities		1
U.S. Treasury securities and obligations of U.S. government authorities and agencies
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	4,950	3,007
Less Than Twelve Months, Gross Unrealized Loss	161	67
Twelve Months or More, Fair Value	267	6,986
Twelve Months or More, Gross Unrealized Losses	0	575
Total, Fair Value	5,217	9,993
Total, Gross Unrealized Losses	161	642
Obligations of U.S. states and their political subdivisions
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	273	1,725
Less Than Twelve Months, Gross Unrealized Loss	8	25
Twelve Months or More, Fair Value	0	999
Twelve Months or More, Gross Unrealized Losses	0	38
Total, Fair Value	273	2,724
Total, Gross Unrealized Losses	8	63
Foreign government bonds
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	2,332	2,369
Less Than Twelve Months, Gross Unrealized Loss	60	136
Twelve Months or More, Fair Value	126	3,515
Twelve Months or More, Gross Unrealized Losses	3	178
Total, Fair Value	2,458	5,884
Total, Gross Unrealized Losses	63	314
U.S. public corporate securities
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	3,944	34,064
Less Than Twelve Months, Gross Unrealized Loss	85	1,570
Twelve Months or More, Fair Value	2,203	13,245
Twelve Months or More, Gross Unrealized Losses	172	1,184
Total, Fair Value	6,147	47,309
Total, Gross Unrealized Losses	257	2,754
U.S. private corporate securities
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	2,283	8,923
Less Than Twelve Months, Gross Unrealized Loss	44	225
Twelve Months or More, Fair Value	1,563	7,985
Twelve Months or More, Gross Unrealized Losses	76	356
Total, Fair Value	3,846	16,908
Total, Gross Unrealized Losses	120	581
Foreign public corporate securities
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	1,271	7,363
Less Than Twelve Months, Gross Unrealized Loss	23	308
Twelve Months or More, Fair Value	496	2,928
Twelve Months or More, Gross Unrealized Losses	47	223
Total, Fair Value	1,767	10,291
Total, Gross Unrealized Losses	70	531
Foreign private corporate securities
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	1,466	12,218
Less Than Twelve Months, Gross Unrealized Loss	33	692
Twelve Months or More, Fair Value	5,666	4,468
Twelve Months or More, Gross Unrealized Losses	547	525
Total, Fair Value	7,132	16,686
Total, Gross Unrealized Losses	580	1,217
Asset-backed securities
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	3,979	8,255
Less Than Twelve Months, Gross Unrealized Loss	12	70
Twelve Months or More, Fair Value	4,433	669
Twelve Months or More, Gross Unrealized Losses	28	7
Total, Fair Value	8,412	8,924
Total, Gross Unrealized Losses	40	77
Commercial mortgage-backed securities
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	1,193	1,781
Less Than Twelve Months, Gross Unrealized Loss	10	14
Twelve Months or More, Fair Value	164	4,733
Twelve Months or More, Gross Unrealized Losses	4	166
Total, Fair Value	1,357	6,514
Total, Gross Unrealized Losses	14	180
Residential mortgage-backed securities
Debt Securities[Line Items]
Less Than Twelve Months, Fair Value	207	194
Less Than Twelve Months, Gross Unrealized Loss	1	1
Twelve Months or More, Fair Value	88	1,042
Twelve Months or More, Gross Unrealized Losses	1	31
Total, Fair Value	295	1,236
Total, Gross Unrealized Losses	$ 2	$ 32