Consolidating Financial Statements (Details) - Consolidating Statement of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Consolidating Statement of Cash Flows
Net income	$ 396	$ 709	$ 1,749	$ 1,902
Net adjustments to reconcile net income to net cash provided by operating activities			2,044	1,530
Net cash provided by operating activities			3,793	3,432
Proceeds from maturities of fixed maturities			4,895	5,655
Proceeds from sales of investments:
Fixed maturities			1,801	3,185
Equity securities			99	127
Real estate investments			0	8
Other investments			346	270
Purchases of investments:
Fixed maturities			(8,234)	(10,862)
Equity securities			(62)	(86)
Real estate investments			(95)	(57)
Other investments			(369)	(392)
Net sales (purchases) of short-term securities			(617)	456
Securities transactions in course of settlement			432	173
Acquisition, net of cash acquired			0	(4)
Other investing activities			(243)	(232)
Net cash used in investing activities			(2,047)	(1,759)
Treasury stock acquired — share repurchase authorization			(1,125)	(1,100)
Treasury stock acquired — net employee share-based compensation			(47)	(51)
Dividends paid to shareholders			(633)	(611)
Payment of debt			(500)	(600)
Issuance of debt			492	591
Issuance of common stock — employee share options			206	117
Dividends paid to parent company			0	0
Net cash used in financing activities			(1,607)	(1,654)
Effect of exchange rate changes on cash			(4)	(4)
Net increase in cash			135	15
Cash at beginning of year			373	344
Cash at end of period	508	359	508	359
Income taxes paid (received)			367	244
Interest paid			231	225
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Cash Flows
Net income	362	559	1,499	1,568
Net adjustments to reconcile net income to net cash provided by operating activities			1,502	1,156
Net cash provided by operating activities			3,001	2,724
Proceeds from maturities of fixed maturities			3,404	4,197
Proceeds from sales of investments:
Fixed maturities			1,142	2,219
Equity securities			42	39
Real estate investments				0
Other investments			261	198
Purchases of investments:
Fixed maturities			(5,551)	(7,625)
Equity securities			(1)	(3)
Real estate investments			0	(1)
Other investments			(323)	(329)
Net sales (purchases) of short-term securities			(630)	364
Securities transactions in course of settlement			312	113
Acquisition, net of cash acquired				0
Other investing activities			(239)	(225)
Net cash used in investing activities			(1,583)	(1,053)
Treasury stock acquired — share repurchase authorization			0	0
Treasury stock acquired — net employee share-based compensation			0	0
Dividends paid to shareholders			0	0
Payment of debt			0	0
Issuance of debt			0	0
Issuance of common stock — employee share options			0	0
Dividends paid to parent company			(1,379)	(1,653)
Net cash used in financing activities			(1,379)	(1,653)
Effect of exchange rate changes on cash			0	(1)
Net increase in cash			39	17
Cash at beginning of year			181	157
Cash at end of period	220	174	220	174
Income taxes paid (received)			333	198
Interest paid			40	40
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Cash Flows
Net income	84	172	376	460
Net adjustments to reconcile net income to net cash provided by operating activities			604	373
Net cash provided by operating activities			980	833
Proceeds from maturities of fixed maturities			1,482	1,439
Proceeds from sales of investments:
Fixed maturities			658	965
Equity securities			57	82
Real estate investments				8
Other investments			85	72
Purchases of investments:
Fixed maturities			(2,670)	(3,215)
Equity securities			(57)	(74)
Real estate investments			(95)	(56)
Other investments			(46)	(63)
Net sales (purchases) of short-term securities			101	209
Securities transactions in course of settlement			120	60
Acquisition, net of cash acquired				(4)
Other investing activities			(4)	(7)
Net cash used in investing activities			(369)	(584)
Treasury stock acquired — share repurchase authorization			0	0
Treasury stock acquired — net employee share-based compensation			0	0
Dividends paid to shareholders			0	0
Payment of debt			(32)	0
Issuance of debt			0	7
Issuance of common stock — employee share options			0	0
Dividends paid to parent company			(479)	(255)
Net cash used in financing activities			(511)	(248)
Effect of exchange rate changes on cash			(4)	(3)
Net increase in cash			96	(2)
Cash at beginning of year			192	187
Cash at end of period	288	185	288	185
Income taxes paid (received)			118	172
Interest paid			0	0
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Statement of Cash Flows
Net income	396	709	1,749	1,902
Net adjustments to reconcile net income to net cash provided by operating activities			(47)	(126)
Net cash provided by operating activities			1,702	1,776
Proceeds from maturities of fixed maturities			9	19
Proceeds from sales of investments:
Fixed maturities			1	1
Equity securities			0	6
Real estate investments				0
Other investments			0	0
Purchases of investments:
Fixed maturities			(13)	(22)
Equity securities			(4)	(9)
Real estate investments			0	0
Other investments			0	0
Net sales (purchases) of short-term securities			(88)	(117)
Securities transactions in course of settlement			0	0
Acquisition, net of cash acquired				0
Other investing activities			0	0
Net cash used in investing activities			(95)	(122)
Treasury stock acquired — share repurchase authorization			(1,125)	(1,100)
Treasury stock acquired — net employee share-based compensation			(47)	(51)
Dividends paid to shareholders			(633)	(611)
Payment of debt			(500)	(600)
Issuance of debt			492	591
Issuance of common stock — employee share options			206	117
Dividends paid to parent company			0	0
Net cash used in financing activities			(1,607)	(1,654)
Effect of exchange rate changes on cash			0	0
Net increase in cash			0	0
Cash at beginning of year			0	0
Cash at end of period	0	0	0	0
Income taxes paid (received)			(84)	(126)
Interest paid			191	185
Eliminations [Member]
Consolidating Statement of Cash Flows
Net income	(446)	(731)	(1,875)	(2,028)
Net adjustments to reconcile net income to net cash provided by operating activities			(15)	127
Net cash provided by operating activities			(1,890)	(1,901)
Proceeds from maturities of fixed maturities			0	0
Proceeds from sales of investments:
Fixed maturities			0	0
Equity securities			0	0
Real estate investments				0
Other investments			0	0
Purchases of investments:
Fixed maturities			0	0
Equity securities			0	0
Real estate investments			0	0
Other investments			0	0
Net sales (purchases) of short-term securities			0	0
Securities transactions in course of settlement			0	0
Acquisition, net of cash acquired				0
Other investing activities			0	0
Net cash used in investing activities			0	0
Treasury stock acquired — share repurchase authorization			0	0
Treasury stock acquired — net employee share-based compensation			0	0
Dividends paid to shareholders			0	0
Payment of debt			32	0
Issuance of debt			0	(7)
Issuance of common stock — employee share options			0	0
Dividends paid to parent company			1,858	1,908
Net cash used in financing activities			1,890	1,901
Effect of exchange rate changes on cash			0	0
Net increase in cash			0	0
Cash at beginning of year			0	0
Cash at end of period	$ 0	$ 0	0	0
Income taxes paid (received)			0	0
Interest paid			$ 0	$ 0