Consolidating Financial Statements (Details) - Consolidating Statement of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Consolidating Statement of Cash Flows
Net income	$ 621	$ 709	$ 524	$ 669	$ 551	$ 293	$ 595	$ 617	$ 2,523	$ 2,056	$ 3,014
Net adjustments to reconcile net income to net cash provided by operating activities									1,857	2,092	1,455
Net cash provided by operating activities									4,380	4,148	4,469
Proceeds from maturities of fixed maturities									7,086	8,750	8,975
Proceeds from sales of investments:
Fixed maturities									3,546	1,854	1,417
Equity securities									178
Equity securities										765	92
Real estate investments									74	23	69
Other investments									511	468	566
Purchases of investments:
Fixed maturities									(13,526)	(12,250)	(11,609)
Equity securities									(117)
Equity securities										(459)	(51)
Real estate investments									(74)	(59)	(48)
Other investments									(537)	(541)	(580)
Net sales (purchases) of short-term securities									908	(26)	(199)
Securities transactions in the course of settlement									(56)	(47)	(21)
Acquisition, net of cash acquired									(4)	(439)
Other investing activities									(318)	(241)	(338)
Net cash used in investing activities									(2,329)	(2,202)	(1,727)
Treasury stock acquired — share repurchase authorization									(1,270)	(1,378)	(2,400)
Treasury stock acquired — net employee share-based compensation									(51)	(62)	(72)
Dividends paid to shareholders									(814)	(785)	(757)
Payment of debt									(600)	(657)	(400)
Issuance of debt									591	789	491
Issuance of common stock -- employee share options									132	173	332
Net cash used in financing activities									(2,012)	(1,920)	(2,806)
Effect of exchange rate changes on cash									(10)	11	(9)
Net increase (decrease) in cash									29	37	(73)
Cash at beginning of year				344				307	344	307	380
Cash at end of year	373				344				373	344	307
Income taxes paid (received)									408	514	892
Interest paid									347	367	358
TRV [Member]
Consolidating Statement of Cash Flows
Net income									2,523	2,064	3,014
Net cash provided by operating activities									2,160	2,032	2,892
Purchases of investments:
Net sales (purchases) of short-term securities									(141)	397	(81)
Acquisition, net of cash acquired										(477)
Net cash used in investing activities									(148)	(114)	(86)
Treasury stock acquired — share repurchase authorization									(1,270)	(1,378)	(2,400)
Treasury stock acquired — net employee share-based compensation									(51)	(62)	(72)
Dividends paid to shareholders									(814)	(785)	(757)
Payment of debt									(600)	(657)	(400)
Issuance of debt									591	789	491
Issuance of common stock -- employee share options									132	173	332
Net cash used in financing activities									(2,012)	(1,920)	(2,806)
Net increase (decrease) in cash										(2)
Cash at beginning of year								2		2	2
Cash at end of year											2
Income taxes paid (received)									(283)	(173)	(132)
Interest paid									300	320	311
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Cash Flows
Net income									2,110	1,728	2,184
Net adjustments to reconcile net income to net cash provided by operating activities									1,141	1,500	1,282
Net cash provided by operating activities									3,251	3,228	3,466
Proceeds from maturities of fixed maturities									5,158	6,576	6,589
Proceeds from sales of investments:
Fixed maturities									2,449	1,007	768
Equity securities									65
Equity securities										97	47
Real estate investments									66
Other investments									403	357	386
Purchases of investments:
Fixed maturities									(9,404)	(8,513)	(7,921)
Equity securities									(8)
Equity securities										(68)	(6)
Real estate investments									(1)	(1)	(1)
Other investments									(454)	(444)	(453)
Net sales (purchases) of short-term securities									895	(303)	(501)
Securities transactions in the course of settlement									(80)	(55)	12
Other investing activities									(310)	(244)	(331)
Net cash used in investing activities									(1,221)	(1,591)	(1,411)
Dividends paid to parent company									(2,003)	(1,624)	(2,140)
Net cash used in financing activities									(2,003)	(1,624)	(2,140)
Effect of exchange rate changes on cash									(3)	3	1
Net increase (decrease) in cash									24	16	(84)
Cash at beginning of year				157				141	157	141	225
Cash at end of year	181				157				181	157	141
Income taxes paid (received)									437	481	737
Interest paid									47	47	47
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Cash Flows
Net income									604	462	970
Net adjustments to reconcile net income to net cash provided by operating activities									605	701	139
Net cash provided by operating activities									1,209	1,163	1,109
Proceeds from maturities of fixed maturities									1,906	2,168	2,380
Proceeds from sales of investments:
Fixed maturities									1,096	846	647
Equity securities									107
Equity securities										414	45
Real estate investments									8	23	69
Other investments									108	124	180
Purchases of investments:
Fixed maturities									(4,096)	(3,697)	(3,676)
Equity securities									(99)
Equity securities										(133)	(42)
Real estate investments									(73)	(58)	(47)
Other investments									(83)	(97)	(127)
Net sales (purchases) of short-term securities									154	(120)	383
Securities transactions in the course of settlement									24	5	(32)
Acquisition, net of cash acquired									(4)	25
Other investing activities									(8)	3	(10)
Net cash used in investing activities									(960)	(497)	(230)
Issuance of debt									18	14
Dividends paid to parent company									(255)	(665)	(858)
Net cash used in financing activities									(237)	(651)	(858)
Effect of exchange rate changes on cash									(7)	8	(10)
Net increase (decrease) in cash									5	23	11
Cash at beginning of year				$ 187				164	187	164	153
Cash at end of year	$ 192				$ 187				192	187	164
Income taxes paid (received)									254	206	287
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Statement of Cash Flows
Net income									2,523	2,064	3,014
Net adjustments to reconcile net income to net cash provided by operating activities									(363)	(32)	(122)
Net cash provided by operating activities									2,160	2,032	2,892
Proceeds from maturities of fixed maturities									22	6	6
Proceeds from sales of investments:
Fixed maturities									1	1	2
Equity securities									6
Equity securities										254
Purchases of investments:
Fixed maturities									(26)	(40)	(12)
Equity securities									(10)
Equity securities										(258)	(3)
Net sales (purchases) of short-term securities									(141)	397	(81)
Securities transactions in the course of settlement										3	(1)
Acquisition, net of cash acquired										(477)
Other investing activities											3
Net cash used in investing activities									(148)	(114)	(86)
Treasury stock acquired — share repurchase authorization									(1,270)	(1,378)	(2,400)
Treasury stock acquired — net employee share-based compensation									(51)	(62)	(72)
Dividends paid to shareholders									(814)	(785)	(757)
Payment of debt									(600)	(657)	(400)
Issuance of debt									591	789	491
Issuance of common stock -- employee share options									132	173	332
Net cash used in financing activities									(2,012)	(1,920)	(2,806)
Net increase (decrease) in cash										(2)
Cash at beginning of year								$ 2		2	2
Cash at end of year											2
Income taxes paid (received)									(283)	(173)	(132)
Interest paid									300	320	311
Eliminations [Member]
Consolidating Statement of Cash Flows
Net income									(2,714)	(2,198)	(3,154)
Net adjustments to reconcile net income to net cash provided by operating activities									474	(77)	156
Net cash provided by operating activities									(2,240)	(2,275)	(2,998)
Proceeds from sales of investments:
Other investments										(13)
Purchases of investments:
Acquisition, net of cash acquired										13
Issuance of debt									(18)	(14)
Dividends paid to parent company									2,258	2,289	2,998
Net cash used in financing activities									$ 2,240	$ 2,275	$ 2,998