Consolidating Financial Statements (details) - Consolidating Statement of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Consolidating Statement of Cash Flows
Net income	$ 595	$ 664	$ 1,212	$ 1,355
Net adjustments to reconcile net income to net cash provided by (used in) operating activities			373	(62)
Net cash provided by operating activities			1,585	1,293
Proceeds from maturities of fixed maturities			4,300	3,773
Proceeds from sales of investments, fixed maturities			563	739
Proceeds from sales of investments, equity securities			200	38
Proceeds from sales of investments, real estate investments			20	69
Proceeds from sales of investments, other investments			403	343
Purchases of investments, fixed maturities			(5,673)	(5,705)
Purchases of investments, equity securities			(166)	(26)
Purchases of investments, real estate investments			(26)	(20)
Purchases of investments, other investments			(259)	(290)
Net (purchases) sales of short-term securities			(424)	681
Securities transactions in course of settlement			170	461
Other investing activities			(129)	(154)
Net cash used in investing activities			(1,021)	(91)
Treasury stock acquired - share repurchase authorization			(700)	(1,100)
Treasury stock acquired - net employee share-based compensation			(61)	(59)
Dividends paid to shareholders			(389)	(375)
Payment of debt			(207)	(400)
Issuance of debt			689	491
Issuance of common stock - employee share options			118	129
Net cash used in financing activities			(550)	(1,314)
Effect of exchange rate changes on cash			7	(3)
Net increase (decrease) in cash			21	(115)
Cash at beginning of year			307	380
Cash at end of period	328	265	328	265
Income taxes paid (received)			323	467
Interest paid			178	180
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Cash Flows
Net income	438	502	946	1,027
Net adjustments to reconcile net income to net cash provided by (used in) operating activities			224	(17)
Net cash provided by operating activities			1,170	1,010
Proceeds from maturities of fixed maturities			3,211	2,728
Proceeds from sales of investments, fixed maturities			285	385
Proceeds from sales of investments, equity securities			4	10
Proceeds from sales of investments, other investments			294	233
Purchases of investments, fixed maturities			(4,160)	(3,588)
Purchases of investments, equity securities			(3)	(5)
Purchases of investments, other investments			(202)	(221)
Net (purchases) sales of short-term securities			383	193
Securities transactions in course of settlement			105	325
Other investing activities			(135)	(151)
Net cash used in investing activities			(218)	(91)
Dividends paid to parent company			(961)	(1,025)
Net cash used in financing activities			(961)	(1,025)
Effect of exchange rate changes on cash			2	2
Net increase (decrease) in cash			(7)	(104)
Cash at beginning of year			141	225
Cash at end of period	134	121	134	121
Income taxes paid (received)			336	398
Interest paid			24	24
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Cash Flows
Net income	162	203	306	408
Net adjustments to reconcile net income to net cash provided by (used in) operating activities			31	(222)
Net cash provided by operating activities			337	186
Proceeds from maturities of fixed maturities			1,087	1,040
Proceeds from sales of investments, fixed maturities			278	352
Proceeds from sales of investments, equity securities			75	28
Proceeds from sales of investments, real estate investments			20	69
Proceeds from sales of investments, other investments			109	110
Purchases of investments, fixed maturities			(1,511)	(2,108)
Purchases of investments, equity securities			(41)	(19)
Purchases of investments, real estate investments			(26)	(20)
Purchases of investments, other investments			(57)	(69)
Net (purchases) sales of short-term securities			78	639
Securities transactions in course of settlement			64	137
Other investing activities			6	(3)
Net cash used in investing activities			82	156
Dividends paid to parent company			(396)	(349)
Net cash used in financing activities			(396)	(349)
Effect of exchange rate changes on cash			5	(5)
Net increase (decrease) in cash			28	(12)
Cash at beginning of year			164	153
Cash at end of period	192	141	192	141
Income taxes paid (received)			119	142
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Statement of Cash Flows
Net income	595	664	1,212	1,355
Net adjustments to reconcile net income to net cash provided by (used in) operating activities			223	116
Net cash provided by operating activities			1,435	1,471
Proceeds from maturities of fixed maturities			2	5
Proceeds from sales of investments, fixed maturities				2
Proceeds from sales of investments, equity securities			121
Purchases of investments, fixed maturities			(2)	(9)
Purchases of investments, equity securities			(122)	(2)
Net (purchases) sales of short-term securities			(885)	(151)
Securities transactions in course of settlement			1	(1)
Net cash used in investing activities			(885)	(156)
Treasury stock acquired - share repurchase authorization			(700)	(1,100)
Treasury stock acquired - net employee share-based compensation			(61)	(59)
Dividends paid to shareholders			(389)	(375)
Payment of debt			(207)	(400)
Issuance of debt			689	491
Issuance of common stock - employee share options			118	129
Net cash used in financing activities			(550)	(1,314)
Net increase (decrease) in cash				1
Cash at beginning of year			2	2
Cash at end of period	2	3	2	3
Income taxes paid (received)			(132)	(73)
Interest paid			154	156
Eliminations [Member]
Consolidating Statement of Cash Flows
Net income	$ (600)	$ (705)	(1,252)	(1,435)
Net adjustments to reconcile net income to net cash provided by (used in) operating activities			(105)	61
Net cash provided by operating activities			(1,357)	(1,374)
Dividends paid to parent company			1,357	1,374
Net cash used in financing activities			$ 1,357	$ 1,374