Consolidating Financial Statements (Details) - Consolidating Statement of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Consolidating Statement of Cash Flows
Net income	$ 796	$ 669
Net adjustments to reconcile net income to net cash provided by operating activities	(157)	(115)
Net cash provided by operating activities	639	554
Proceeds from maturities of fixed maturities	1,556	1,950
Proceeds from sales of investments:
Fixed maturities	769	1,085
Equity securities	39	26
Other investments	105	114
Purchases of investments:
Fixed maturities	(2,914)	(3,920)
Equity securities	(22)	(20)
Real estate investments	(77)	(33)
Other investments	(146)	(142)
Net sales (purchases) of short-term securities	(109)	410
Securities transactions in course of settlement	295	202
Other investing activities	(82)	(53)
Net cash used in investing activities	(586)	(381)
Treasury stock acquired — share repurchase authorization	(375)	(350)
Treasury stock acquired — net employee share-based compensation	(46)	(51)
Dividends paid to shareholders	(205)	(197)
Payment of debt		(100)
Issuance of debt	492	491
Issuance of common stock — employee share options	63	85
Net cash used in financing activities	(71)	(122)
Effect of exchange rate changes on cash	2	2
Net increase (decrease) in cash	(16)	53
Cash at beginning of year	373	344
Cash at end of period	357	397
Income taxes paid	5	56
Interest paid	50	39
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Cash Flows
Net income	625	551
Net adjustments to reconcile net income to net cash provided by operating activities	(110)	(126)
Net cash provided by operating activities	515	425
Proceeds from maturities of fixed maturities	1,043	1,453
Proceeds from sales of investments:
Fixed maturities	551	729
Equity securities	19	8
Other investments	90	76
Purchases of investments:
Fixed maturities	(2,228)	(2,836)
Equity securities	(1)	(1)
Other investments	(134)	(115)
Net sales (purchases) of short-term securities	210	729
Securities transactions in course of settlement	283	147
Other investing activities	(80)	(52)
Net cash used in investing activities	(247)	138
Dividends paid to parent company	(300)	(544)
Net cash used in financing activities	(300)	(544)
Effect of exchange rate changes on cash	1	(1)
Net increase (decrease) in cash	(31)	18
Cash at beginning of year	181	157
Cash at end of period	150	175
Income taxes paid	4	13
Interest paid	16	16
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Cash Flows
Net income	208	168
Net adjustments to reconcile net income to net cash provided by operating activities	(42)	(57)
Net cash provided by operating activities	166	111
Proceeds from maturities of fixed maturities	508	493
Proceeds from sales of investments:
Fixed maturities	218	356
Equity securities	20	18
Other investments	15	38
Purchases of investments:
Fixed maturities	(682)	(1,078)
Equity securities	(20)	(18)
Real estate investments	(77)	(33)
Other investments	(12)	(27)
Net sales (purchases) of short-term securities	178	201
Securities transactions in course of settlement	13	56
Other investing activities	(2)	(1)
Net cash used in investing activities	159	5
Payment of debt	(32)
Dividends paid to parent company	(279)	(85)
Net cash used in financing activities	(311)	(85)
Effect of exchange rate changes on cash	1	3
Net increase (decrease) in cash	15	34
Cash at beginning of year	192	187
Cash at end of period	207	221
Income taxes paid	1	43
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Statement of Cash Flows
Net income	796	669
Net adjustments to reconcile net income to net cash provided by operating activities	(227)	(22)
Net cash provided by operating activities	569	647
Proceeds from maturities of fixed maturities	5	4
Purchases of investments:
Fixed maturities	(4)	(6)
Equity securities	(1)	(1)
Net sales (purchases) of short-term securities	(497)	(520)
Securities transactions in course of settlement	(1)	(1)
Net cash used in investing activities	(498)	(524)
Treasury stock acquired — share repurchase authorization	(375)	(350)
Treasury stock acquired — net employee share-based compensation	(46)	(51)
Dividends paid to shareholders	(205)	(197)
Payment of debt		(100)
Issuance of debt	492	491
Issuance of common stock — employee share options	63	85
Net cash used in financing activities	(71)	(122)
Net increase (decrease) in cash		1
Cash at end of period		1
Interest paid	34	23
Eliminations [Member]
Consolidating Statement of Cash Flows
Net income	(833)	(719)
Net adjustments to reconcile net income to net cash provided by operating activities	222	90
Net cash provided by operating activities	(611)	(629)
Purchases of investments:
Payment of debt	32
Dividends paid to parent company	579	629
Net cash used in financing activities	$ 611	$ 629