Consolidating Financial Statements (Details) - Consolidating Balance Sheet (Unaudited) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Consolidating Balance Sheet
Fixed maturities, at fair value	$ 62,424	$ 62,694
Equity securities, at fair value	426
Equity securities, available for sale, at fair value		453
Real estate investments	951	932
Short-term securities	4,437	4,895
Other investments	3,615	3,528
Total investments	71,853	72,502
Cash	359	344	$ 379	$ 307
Investment income accrued	583	606
Premiums receivable	7,639	7,144
Reinsurance recoverables	8,314	8,309
Ceded unearned premiums	715	551
Deferred acquisition costs	2,186	2,025
Deferred taxes	521	70
Contractholder receivables	4,887	4,775
Goodwill	3,958	3,951
Other intangible assets	351	342
Other assets	3,024	2,864
Total assets	104,390	103,483
Claims and claim adjustment expense reserves	50,430	49,650
Unearned premium reserves	13,979	12,915
Contractholder payables	4,887	4,775
Payables for reinsurance premiums	418	274
Debt	6,564	6,571
Other liabilities	5,652	5,567
Total liabilities	81,930	79,752
Common stock	23,089	22,886
Retained earnings	34,799	33,462
Accumulated other comprehensive income (loss)	(2,003)	(343)
Treasury stock, at cost	(33,425)	(32,274)
Total shareholders’ equity	22,460	23,731	23,738
Total liabilities and shareholders’ equity	104,390	103,483
Fixed maturities, available for sale, amortized cost	62,985	61,316
Equity securities, cost	$ 408
Equity securities, available for sale, cost		$ 440
Common stock, shares authorized (in shares)	1,750,000,000.0	1,750,000,000.0
Common stock, shares issued (in shares)	264,900,000	271,500,000
Common stock, shares outstanding (in shares)	264,800,000	271,400,000
Treasury stock, at cost (in shares)	509,500,000	500,900,000
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	$ 42,923	$ 43,240
Equity securities, at fair value	130
Equity securities, available for sale, at fair value		161
Real estate investments	54	54
Short-term securities	2,386	2,751
Other investments	2,779	2,673
Total investments	48,272	48,879
Cash	174	157	165	141
Investment income accrued	403	418
Premiums receivable	5,182	4,852
Reinsurance recoverables	5,812	5,842
Ceded unearned premiums	635	493
Deferred acquisition costs	1,986	1,835
Deferred taxes	239	(89)
Contractholder receivables	3,960	3,854
Goodwill	2,586	2,592
Other intangible assets	225	202
Other assets	2,068	2,181
Total assets	71,542	71,216
Claims and claim adjustment expense reserves	33,862	33,386
Unearned premium reserves	9,735	8,957
Contractholder payables	3,960	3,854
Payables for reinsurance premiums	250	165
Debt	693	693
Other liabilities	4,287	4,161
Total liabilities	52,787	51,216
Additional paid-in capital	11,634	11,634
Retained earnings	7,883	8,036
Accumulated other comprehensive income (loss)	(762)	330
Total shareholders’ equity	18,755	20,000
Total liabilities and shareholders’ equity	71,542	71,216
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	19,419	19,372
Equity securities, at fair value	105
Equity securities, available for sale, at fair value		111
Real estate investments	897	878
Short-term securities	704	914
Other investments	835	854
Total investments	21,960	22,129
Cash	185	187	$ 214	164
Investment income accrued	176	183
Premiums receivable	2,457	2,292
Reinsurance recoverables	2,502	2,467
Ceded unearned premiums	80	58
Deferred acquisition costs	200	190
Deferred taxes	339	173
Contractholder receivables	927	921
Goodwill	1,381	1,368
Other intangible assets	126	140
Other assets	452	(3)
Total assets	30,785	30,105
Claims and claim adjustment expense reserves	16,568	16,264
Unearned premium reserves	4,244	3,958
Contractholder payables	927	921
Payables for reinsurance premiums	168	109
Debt	21	14
Other liabilities	1,188	882
Total liabilities	23,116	22,148
Common stock	390	390
Additional paid-in capital	6,986	6,972
Retained earnings	772	594
Accumulated other comprehensive income (loss)	(479)	1
Total shareholders’ equity	7,669	7,957
Total liabilities and shareholders’ equity	30,785	30,105
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	82	82
Equity securities, at fair value	191
Equity securities, available for sale, at fair value		181
Short-term securities	1,347	1,230
Other investments	1	1
Total investments	1,621	1,494
Cash				$ 2
Investment income accrued	4	5
Deferred taxes	(57)	(14)
Investment in subsidiaries	26,412	27,946
Other assets	525	700
Total assets	28,505	30,131
Debt	5,871	5,878
Other liabilities	177	524
Total liabilities	6,048	6,402
Common stock	23,089	22,886
Retained earnings	34,796	33,460
Accumulated other comprehensive income (loss)	(2,003)	(343)
Treasury stock, at cost	(33,425)	(32,274)
Total shareholders’ equity	22,457	23,729
Total liabilities and shareholders’ equity	28,505	30,131
Eliminations [Member]
Consolidating Balance Sheet
Goodwill	(9)	(9)
Investment in subsidiaries	(26,412)	(27,946)
Other assets	(21)	(14)
Total assets	(26,442)	(27,969)
Debt	(21)	(14)
Total liabilities	(21)	(14)
Common stock	(390)	(390)
Additional paid-in capital	(18,620)	(18,606)
Retained earnings	(8,652)	(8,628)
Accumulated other comprehensive income (loss)	1,241	(331)
Total shareholders’ equity	(26,421)	(27,955)
Total liabilities and shareholders’ equity	$ (26,442)	$ (27,969)