Consolidating Financial Statements (details) - Consolidating Balance Sheet (Unaudited) - USD ($) shares in Millions, $ in Millions	Sep. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Dec. 31, 2015
Consolidating Balance Sheet
Fixed maturities, available for sale, at fair value	$ 62,157	$ 60,515
Equity securities, available for sale, at fair value	601	732
Real estate investments	923	928
Short-term securities	5,859	4,865
Other investments	3,552	3,448
Total investments	73,092	70,488
Cash	379	307	$ 269	$ 380
Investment income accrued	568	630
Premiums receivable	7,267	6,722
Reinsurance recoverables	8,345	8,287
Ceded unearned premiums	688	589
Deferred acquisition costs	2,077	1,923
Deferred taxes	243	465
Contractholder receivables	4,757	4,609
Goodwill	3,946	3,580
Other intangible assets	345	268
Other assets	2,604	2,377
Total assets	104,311	100,245
Claims and claim adjustment expense reserves	49,750	47,949
Unearned premium reserves	13,247	12,329
Contractholder payables	4,757	4,609
Payables for reinsurance premiums	423	273
Debt	6,921	6,437
Other liabilities	5,475	5,427
Total liabilities	80,573	77,024
Common stock	22,836	22,614
Retained earnings	33,110	32,196
Accumulated other comprehensive income (loss)	(285)	(755)
Treasury stock, at cost	(31,923)	(30,834)
Total shareholders' equity	23,738	23,221	24,439
Total liabilities and shareholders' equity	104,311	100,245
Fixed maturities, available for sale, amortized cost	60,727	59,650
Equity securities, available for sale, cost	$ 509	$ 504
Common stock, shares authorized (in shares)	1,750.0	1,750.0
Common stock, shares issued (in shares)	273.8	279.6
Common stock, shares outstanding (in shares)	273.7	279.6
Treasury stock, at cost (in shares)	498.3	489.5
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Balance Sheet
Fixed maturities, available for sale, at fair value	$ 42,889	$ 42,014
Equity securities, available for sale, at fair value	173	169
Real estate investments	55	56
Short-term securities	2,936	2,447
Other investments	2,666	2,569
Total investments	48,719	47,255
Cash	165	141	131	225
Investment income accrued	392	441
Premiums receivable	4,938	4,545
Reinsurance recoverables	5,791	5,664
Ceded unearned premiums	612	536
Deferred acquisition costs	1,880	1,741
Deferred taxes	(76)	216
Contractholder receivables	3,813	3,656
Goodwill	2,593	2,578
Other intangible assets	202	202
Other assets	2,247	1,973
Total assets	71,276	68,948
Claims and claim adjustment expense reserves	33,358	32,168
Unearned premium reserves	9,225	8,575
Contractholder payables	3,813	3,656
Payables for reinsurance premiums	249	156
Debt	693	693
Other liabilities	3,946	4,106
Total liabilities	51,284	49,354
Additional paid-in capital	11,634	11,634
Retained earnings	7,989	7,933
Accumulated other comprehensive income (loss)	369	27
Total shareholders' equity	19,992	19,594
Total liabilities and shareholders' equity	71,276	68,948
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Balance Sheet
Fixed maturities, available for sale, at fair value	19,218	18,452
Equity securities, available for sale, at fair value	255	408
Real estate investments	868	872
Short-term securities	1,024	791
Other investments	885	878
Total investments	22,250	21,401
Cash	214	164	136	153
Investment income accrued	170	183
Premiums receivable	2,329	2,177
Reinsurance recoverables	2,554	2,623
Ceded unearned premiums	76	53
Deferred acquisition costs	197	182
Deferred taxes	224	224
Contractholder receivables	944	953
Goodwill	1,362	1,002
Other intangible assets	143	66
Other assets	91	370
Total assets	30,554	29,398
Claims and claim adjustment expense reserves	16,392	15,781
Unearned premium reserves	4,022	3,754
Contractholder payables	944	953
Payables for reinsurance premiums	174	117
Other liabilities	967	1,239
Total liabilities	22,499	21,844
Common stock	390	390
Additional paid-in capital	6,970	6,499
Retained earnings	683	797
Accumulated other comprehensive income (loss)	12	(132)
Total shareholders' equity	8,055	7,554
Total liabilities and shareholders' equity	30,554	29,398
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Balance Sheet
Fixed maturities, available for sale, at fair value	50	49
Equity securities, available for sale, at fair value	173	155
Short-term securities	1,899	1,627
Other investments	1	1
Total investments	2,123	1,832
Cash		2	$ 2	$ 2
Investment income accrued	6	6
Deferred taxes	95	25
Investment in subsidiaries	28,036	27,137
Other assets	266	34
Total assets	30,526	29,036
Debt	6,228	5,744
Other liabilities	562	82
Total liabilities	6,790	5,826
Common stock	22,836	22,614
Retained earnings	33,108	32,185
Accumulated other comprehensive income (loss)	(285)	(755)
Treasury stock, at cost	(31,923)	(30,834)
Total shareholders' equity	23,736	23,210
Total liabilities and shareholders' equity	30,526	29,036
Eliminations [Member]
Consolidating Balance Sheet
Goodwill	(9)
Investment in subsidiaries	(28,036)	(27,137)
Total assets	(28,045)	(27,137)
Common stock	(390)	(390)
Additional paid-in capital	(18,604)	(18,133)
Retained earnings	(8,670)	(8,719)
Accumulated other comprehensive income (loss)	(381)	105
Total shareholders' equity	(28,045)	(27,137)
Total liabilities and shareholders' equity	$ (28,045)	$ (27,137)