Consolidating Financial Statements (Details) - Consolidating Balance Sheet (Unaudited) - USD ($) $ in Millions	Jun. 30, 2018	Dec. 31, 2017	Jun. 30, 2017	Dec. 31, 2016
Consolidating Balance Sheet
Fixed maturities, at fair value	$ 62,536	$ 62,694
Equity securities, at fair value	424
Equity securities, available for sale, at fair value		453
Real estate investments	954	932
Short-term securities	3,692	4,895
Other investments	3,555	3,528
Total investments	71,161	72,502
Cash	415	344	$ 328	$ 307
Investment income accrued	610	606
Premiums receivable	7,786	7,144
Reinsurance recoverables	8,258	8,309
Ceded unearned premiums	698	551
Deferred acquisition costs	2,161	2,025
Deferred taxes	463	70
Contractholder receivables	4,830	4,775
Goodwill	3,931	3,951
Other intangible assets	356	342
Other assets	2,854	2,864
Total assets	103,523	103,483
Claims and claim adjustment expense reserves	49,961	49,650
Unearned premium reserves	13,755	12,915
Contractholder payables	4,830	4,775
Payables for reinsurance premiums	396	274
Debt	6,464	6,571
Other liabilities	5,494	5,567
Total liabilities	80,900	79,752
Common stock	23,040	22,886
Retained earnings	34,296	33,462
Accumulated other comprehensive income (loss)	(1,688)	(343)
Treasury stock, at cost	(33,025)	(32,274)
Total shareholders’ equity	22,623	23,731	23,858
Total liabilities and shareholders’ equity	103,523	103,483
Fixed maturities, available for sale, amortized cost	62,674	61,316
Equity securities, cost	$ 409
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)	267,800,000	271,500,000
Common stock, shares outstanding (in shares)	267,700,000	271,400,000
Treasury stock, at cost (in shares)	506,400,000	500,900,000
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	$ 43,192	$ 43,240
Equity securities, at fair value	131
Equity securities, available for sale, at fair value		161
Real estate investments	54	54
Short-term securities	1,765	2,751
Other investments	2,730	2,673
Total investments	47,872	48,879
Cash	231	157	134	141
Investment income accrued	424	418
Premiums receivable	5,251	4,852
Reinsurance recoverables	5,797	5,842
Ceded unearned premiums	610	493
Deferred acquisition costs	1,955	1,835
Deferred taxes	180	(89)
Contractholder receivables	3,909	3,854
Goodwill	2,584	2,592
Other intangible assets	225	202
Other assets	2,077	2,181
Total assets	71,115	71,216
Claims and claim adjustment expense reserves	33,579	33,386
Unearned premium reserves	9,542	8,957
Contractholder payables	3,909	3,854
Payables for reinsurance premiums	230	165
Debt	693	693
Other liabilities	4,188	4,161
Total liabilities	52,141	51,216
Additional paid-in capital	11,634	11,634
Retained earnings	7,869	8,036
Accumulated other comprehensive income (loss)	(529)	330
Total shareholders’ equity	18,974	20,000
Total liabilities and shareholders’ equity	71,115	71,216
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	19,260	19,372
Equity securities, at fair value	110
Equity securities, available for sale, at fair value		111
Real estate investments	900	878
Short-term securities	530	914
Other investments	824	854
Total investments	21,624	22,129
Cash	184	187	192	164
Investment income accrued	182	183
Premiums receivable	2,535	2,292
Reinsurance recoverables	2,461	2,467
Ceded unearned premiums	88	58
Deferred acquisition costs	206	190
Deferred taxes	295	173
Contractholder receivables	921	921
Goodwill	1,356	1,368
Other intangible assets	131	140
Other assets	166	(3)
Total assets	30,149	30,105
Claims and claim adjustment expense reserves	16,382	16,264
Unearned premium reserves	4,213	3,958
Contractholder payables	921	921
Payables for reinsurance premiums	166	109
Debt	21	14
Other liabilities	778	882
Total liabilities	22,481	22,148
Common stock	390	390
Additional paid-in capital	6,972	6,972
Retained earnings	685	594
Accumulated other comprehensive income (loss)	(379)	1
Total shareholders’ equity	7,668	7,957
Total liabilities and shareholders’ equity	30,149	30,105
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	84	82
Equity securities, at fair value	183
Equity securities, available for sale, at fair value		181
Short-term securities	1,397	1,230
Other investments	1	1
Total investments	1,665	1,494
Cash			$ 2	$ 2
Investment income accrued	4	5
Deferred taxes	(12)	(14)
Investment in subsidiaries	26,630	27,946
Other assets	632	700
Total assets	28,919	30,131
Debt	5,771	5,878
Other liabilities	528	524
Total liabilities	6,299	6,402
Common stock	23,040	22,886
Retained earnings	34,293	33,460
Accumulated other comprehensive income (loss)	(1,688)	(343)
Treasury stock, at cost	(33,025)	(32,274)
Total shareholders’ equity	22,620	23,729
Total liabilities and shareholders’ equity	28,919	30,131
Eliminations [Member]
Consolidating Balance Sheet
Goodwill	(9)	(9)
Investment in subsidiaries	(26,630)	(27,946)
Other assets	(21)	(14)
Total assets	(26,660)	(27,969)
Debt	(21)	(14)
Total liabilities	(21)	(14)
Common stock	(390)	(390)
Additional paid-in capital	(18,606)	(18,606)
Retained earnings	(8,551)	(8,628)
Accumulated other comprehensive income (loss)	908	(331)
Total shareholders’ equity	(26,639)	(27,955)
Total liabilities and shareholders’ equity	$ (26,660)	$ (27,969)