Reinsurance (Details) - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts, life insurance in force	$ 104,726	$ 99,888	$ 95,533
Gross amounts	5,251	5,052	4,857
Ceded amounts to other companies, life insurance in force	38,584	38,711	38,724
Ceded Premiums Earned	230	230	224
Assumed amounts from other companies, life insurance in force	0	0	0
Assumed amounts from other companies	149	132	77
Net amounts, life insurance in force	66,142	61,177	56,808
Premiums Earned, Net	$ 5,170	$ 4,954	$ 4,710
Percentage of amounts assumed to net, life insurance in force	0.00%	0.00%	0.00%
Percentage of amounts assumed to net	2.90%	2.70%	1.60%
Commercial Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	$ 3,314	$ 3,258	$ 3,180
Ceded Premiums Earned	104	99	98
Assumed amounts from other companies	8	6	7
Premiums Earned, Net	$ 3,218	$ 3,165	$ 3,089
Percentage of amounts assumed to net	0.30%	0.20%	0.20%
Personal Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	$ 1,372	$ 1,275	$ 1,195
Ceded Premiums Earned	37	35	35
Assumed amounts from other companies	1	1	1
Premiums Earned, Net	$ 1,336	$ 1,241	$ 1,161
Percentage of amounts assumed to net	0.10%	0.10%	0.10%
Excess and Surplus Lines Insurance
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	$ 245	$ 219	$ 192
Ceded Premiums Earned	11	10	9
Assumed amounts from other companies	0	0	0
Premiums Earned, Net	$ 234	$ 209	$ 183
Percentage of amounts assumed to net	0.00%	0.00%	0.00%
Reinsurance assumed and other non segment [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	$ 0	$ 0	$ 0
Ceded Premiums Earned	8	18	20
Assumed amounts from other companies	140	125	69
Premiums Earned, Net	$ 132	$ 107	$ 49
Percentage of amounts assumed to net	106.10%	116.10%	140.80%
Property, Liability And Casualty Insurance Segment [Member]
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	$ 4,931	$ 4,752	$ 4,567
Ceded Premiums Earned	160	162	162
Assumed amounts from other companies	149	132	77
Premiums Earned, Net	$ 4,920	$ 4,722	$ 4,482
Percentage of amounts assumed to net	3.00%	2.80%	1.70%
Life Insurance Segment
Reinsurance Premiums for Insurance Companies, by Product Segment [Line Items]
Gross amounts	$ 320	$ 300	$ 290
Ceded Premiums Earned	70	68	62
Assumed amounts from other companies	0	0	0
Premiums Earned, Net	$ 250	$ 232	$ 228
Percentage of amounts assumed to net	0.00%	0.00%	0.00%

Amount of earned premiums assumed from other entities.

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