Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts, life insurance in force	$ 111,756	$ 108,130	$ 104,726
Gross amounts	5,985	5,681	5,251
Ceded amounts to other companies, life insurance in force	38,281	38,146	38,584
Ceded premiums earned	290	276	230
Assumed amounts from other companies, life insurance in force	0	0	0
Assumed amounts from other companies	285	199	149
Net amounts, life insurance in force	73,475	69,984	66,142
Premiums Earned, Net	$ 5,980	$ 5,604	$ 5,170
Percentage of amounts assumed to net, life insurance in force	0.00%	0.00%	0.00%
Percentage of amounts assumed to net	4.80%	3.60%	2.90%
Commercial Insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 3,578	$ 3,421	$ 3,314
Ceded premiums earned	109	109	104
Assumed amounts from other companies	7	7	8
Premiums Earned, Net	$ 3,476	$ 3,319	$ 3,218
Percentage of amounts assumed to net	0.20%	0.20%	0.30%
Personal Insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 1,503	$ 1,446	$ 1,372
Ceded premiums earned	41	43	37
Assumed amounts from other companies	1	1	1
Premiums Earned, Net	$ 1,463	$ 1,404	$ 1,336
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	$ 341	$ 292	$ 245
Ceded premiums earned	16	14	11
Assumed amounts from other companies	0	0	0
Premiums Earned, Net	$ 325	$ 278	$ 234
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	$ 201	$ 181	$ 0
Ceded premiums earned	51	39	8
Assumed amounts from other companies	277	191	140
Premiums Earned, Net	$ 427	$ 333	$ 132
Percentage of amounts assumed to net	64.90%	57.40%	106.10%
Property, Liability and Casualty Insurance
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 5,623	$ 5,340	$ 4,931
Ceded premiums earned	217	205	160
Assumed amounts from other companies	285	199	149
Premiums Earned, Net	$ 5,691	$ 5,334	$ 4,920
Percentage of amounts assumed to net	5.00%	3.70%	3.00%
Life Insurance Segment
SEC Schedule, 12-17, Insurance Companies, Reinsurance
Gross amounts	$ 362	$ 341	$ 320
Ceded premiums earned	73	71	70
Assumed amounts from other companies	0	0	0
Premiums Earned, Net	$ 289	$ 270	$ 250
Percentage of amounts assumed to net	0.00%	0.00%	0.00%