Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts, life insurance in force	$ 108,130	$ 104,726	$ 99,888
Gross amounts	5,681	5,251	5,052
Ceded amounts to other companies, life insurance in force	38,146	38,584	38,711
Ceded premiums earned	276	230	230
Assumed amounts from other companies, life insurance in force	0	0	0
Assumed amounts from other companies	199	149	132
Net amounts, life insurance in force	69,984	66,142	61,177
Premiums Earned, Net	$ 5,604	$ 5,170	$ 4,954
Percentage of amounts assumed to net, life insurance in force	0.00%	0.00%	0.00%
Percentage of amounts assumed to net	3.60%	2.90%	2.70%
Commercial Insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 3,421	$ 3,314	$ 3,258
Ceded premiums earned	109	104	99
Assumed amounts from other companies	7	8	6
Premiums Earned, Net	$ 3,319	$ 3,218	$ 3,165
Percentage of amounts assumed to net	0.20%	0.30%	0.20%
Personal Insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 1,446	$ 1,372	$ 1,275
Ceded premiums earned	43	37	35
Assumed amounts from other companies	1	1	1
Premiums Earned, Net	$ 1,404	$ 1,336	$ 1,241
Percentage of amounts assumed to net	0.10%	0.10%	0.10%
Excess and Surplus Lines Insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 292	$ 245	$ 219
Ceded premiums earned	14	11	10
Assumed amounts from other companies	0	0	0
Premiums Earned, Net	$ 278	$ 234	$ 209
Percentage of amounts assumed to net	0.00%	0.00%	0.00%
Reinsurance assumed and other non segment
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 181	$ 0	$ 0
Ceded premiums earned	39	8	18
Assumed amounts from other companies	191	140	125
Premiums Earned, Net	$ 333	$ 132	$ 107
Percentage of amounts assumed to net	57.40%	106.10%	116.10%
Property, Liability and Casualty Insurance Product Line
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 5,340	$ 4,931	$ 4,752
Ceded premiums earned	205	160	162
Assumed amounts from other companies	199	149	132
Premiums Earned, Net	$ 5,334	$ 4,920	$ 4,722
Percentage of amounts assumed to net	3.70%	3.00%	2.80%
Life Insurance Segment
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 341	$ 320	$ 300
Ceded premiums earned	71	70	68
Assumed amounts from other companies	0	0	0
Premiums Earned, Net	$ 270	$ 250	$ 232
Percentage of amounts assumed to net	0.00%	0.00%	0.00%