Consolidating Financial Statements (Details) - Consolidating Balance Sheet (Unaudited) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017	Mar. 31, 2017	Dec. 31, 2016
Consolidating Balance Sheet
Fixed maturities, at fair value	$ 62,266	$ 62,694
Equity securities, at fair value	430
Equity securities, available for sale, at fair value		453
Real estate investments	954	932
Short-term securities	4,486	4,895
Other investments	3,588	3,528
Total investments	71,724	72,502
Cash	397	344	$ 249	$ 307
Investment income accrued	567	606
Premiums receivable	7,536	7,144
Reinsurance recoverables	8,298	8,309
Ceded unearned premiums	777	551
Deferred acquisition costs	2,086	2,025
Deferred taxes	368	70
Contractholder receivables	4,835	4,775
Goodwill	3,959	3,951
Other intangible assets	341	342
Other assets	2,788	2,864
Total assets	103,676	103,483
Claims and claim adjustment expense reserves	49,810	49,650
Unearned premium reserves	13,424	12,915
Contractholder payables	4,835	4,775
Payables for reinsurance premiums	498	274
Debt	6,963	6,571
Other liabilities	5,167	5,567
Total liabilities	80,697	79,752
Common stock	22,995	22,886
Retained earnings	33,981	33,462
Accumulated other comprehensive income (loss)	(1,322)	(343)
Treasury stock, at cost	(32,675)	(32,274)
Total shareholders’ equity	22,979	23,731	23,612
Total liabilities and shareholders’ equity	103,676	103,483
Fixed maturities, available for sale, amortized cost	62,093	61,316
Equity securities, cost	$ 431
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)	270,300,000	271,500,000
Common stock, shares outstanding (in shares)	270,200,000	271,400,000
Treasury stock, at cost (in shares)	503,700,000	500,900,000
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	$ 42,958	$ 43,240
Equity securities, at fair value	147
Equity securities, available for sale, at fair value		161
Real estate investments	54	54
Short-term securities	2,022	2,751
Other investments	2,745	2,673
Total investments	47,926	48,879
Cash	175	157	91	141
Investment income accrued	388	418
Premiums receivable	5,073	4,852
Reinsurance recoverables	5,823	5,842
Ceded unearned premiums	687	493
Deferred acquisition costs	1,887	1,835
Deferred taxes	115	(89)
Contractholder receivables	3,907	3,854
Goodwill	2,587	2,592
Other intangible assets	201	202
Other assets	2,150	2,181
Total assets	70,919	71,216
Claims and claim adjustment expense reserves	33,447	33,386
Unearned premium reserves	9,336	8,957
Contractholder payables	3,907	3,854
Payables for reinsurance premiums	295	165
Debt	693	693
Other liabilities	3,922	4,161
Total liabilities	51,600	51,216
Additional paid-in capital	11,634	11,634
Retained earnings	7,974	8,036
Accumulated other comprehensive income (loss)	(289)	330
Total shareholders’ equity	19,319	20,000
Total liabilities and shareholders’ equity	70,919	71,216
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	19,225	19,372
Equity securities, at fair value	103
Equity securities, available for sale, at fair value		111
Real estate investments	900	878
Short-term securities	714	914
Other investments	842	854
Total investments	21,784	22,129
Cash	221	187	156	164
Investment income accrued	175	183
Premiums receivable	2,463	2,292
Reinsurance recoverables	2,475	2,467
Ceded unearned premiums	90	58
Deferred acquisition costs	199	190
Deferred taxes	271	173
Contractholder receivables	928	921
Goodwill	1,381	1,368
Other intangible assets	140	140
Other assets	342	(3)
Total assets	30,469	30,105
Claims and claim adjustment expense reserves	16,363	16,264
Unearned premium reserves	4,088	3,958
Contractholder payables	928	921
Payables for reinsurance premiums	203	109
Debt	14	14
Other liabilities	1,091	882
Total liabilities	22,687	22,148
Common stock	390	390
Additional paid-in capital	6,972	6,972
Retained earnings	650	594
Accumulated other comprehensive income (loss)	(230)	1
Total shareholders’ equity	7,782	7,957
Total liabilities and shareholders’ equity	30,469	30,105
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Balance Sheet
Fixed maturities, at fair value	83	82
Equity securities, at fair value	180
Equity securities, available for sale, at fair value		181
Short-term securities	1,750	1,230
Other investments	1	1
Total investments	2,014	1,494
Cash	1		$ 2	$ 2
Investment income accrued	4	5
Deferred taxes	(18)	(14)
Investment in subsidiaries	27,090	27,946
Other assets	310	700
Total assets	29,401	30,131
Debt	6,270	5,878
Other liabilities	154	524
Total liabilities	6,424	6,402
Common stock	22,995	22,886
Retained earnings	33,979	33,460
Accumulated other comprehensive income (loss)	(1,322)	(343)
Treasury stock, at cost	(32,675)	(32,274)
Total shareholders’ equity	22,977	23,729
Total liabilities and shareholders’ equity	29,401	30,131
Eliminations [Member]
Consolidating Balance Sheet
Goodwill	(9)	(9)
Investment in subsidiaries	(27,090)	(27,946)
Other assets	(14)	(14)
Total assets	(27,113)	(27,969)
Debt	(14)	(14)
Total liabilities	(14)	(14)
Common stock	(390)	(390)
Additional paid-in capital	(18,606)	(18,606)
Retained earnings	(8,622)	(8,628)
Accumulated other comprehensive income (loss)	519	(331)
Total shareholders’ equity	(27,099)	(27,955)
Total liabilities and shareholders’ equity	$ (27,113)	$ (27,969)