Consolidating Financial Statements (details) - Consolidating Statement of Cash Flows (Unaudited) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Consolidating Statement of Cash Flows
Net income	$ 293	$ 716	$ 1,505	$ 2,071
Net adjustments to reconcile net income to net cash provided by operating activities			1,719	992
Net cash provided by operating activities			3,224	3,063
Proceeds from maturities of fixed maturities			6,581	6,648
Proceeds from sales of investments, fixed maturities			860	865
Proceeds from sales of investments, equity securities			340	71
Proceeds from sales of investments, real estate investments			23	69
Proceeds from sales of investments, other investments			603	569
Purchases of investments, fixed maturities			(8,403)	(9,004)
Purchases of investments, equity securities			(193)	(36)
Purchases of investments, real estate investments			(40)	(30)
Purchases of investments, other investments			(392)	(422)
Net (purchases) sales of short-term securities			(990)	(135)
Securities transactions in course of settlement			122	511
Acquisition, net of cash acquired			(439)
Other investing activities			(187)	(240)
Net cash used in investing activities			(2,115)	(1,134)
Treasury stock acquired - share repurchase authorization			(1,028)	(1,650)
Treasury stock acquired - net employee share-based compensation			(61)	(71)
Dividends paid to shareholders			(589)	(569)
Payment of debt			(207)	(400)
Issuance of debt			689	491
Issuance of common stock - employee share options			148	164
Net cash used in financing activities			(1,048)	(2,035)
Effect of exchange rate changes on cash			11	(5)
Net increase (decrease) in cash			72	(111)
Cash at beginning of year			307	380
Cash at end of period	379	269	379	269
Income taxes paid (received)			467	648
Interest paid			217	223
Reportable Legal Entities [Member] | TPC [Member]
Consolidating Statement of Cash Flows
Net income	295	538	1,241	1,565
Net adjustments to reconcile net income to net cash provided by operating activities			975	643
Net cash provided by operating activities			2,216	2,208
Proceeds from maturities of fixed maturities			4,961	4,854
Proceeds from sales of investments, fixed maturities			463	458
Proceeds from sales of investments, equity securities			18	39
Proceeds from sales of investments, other investments			426	399
Purchases of investments, fixed maturities			(5,906)	(6,016)
Purchases of investments, equity securities			(5)	(5)
Purchases of investments, real estate investments				(1)
Purchases of investments, other investments			(305)	(328)
Net (purchases) sales of short-term securities			(488)	(339)
Securities transactions in course of settlement			18	422
Other investing activities			(192)	(236)
Net cash used in investing activities			(1,010)	(753)
Dividends paid to parent company			(1,185)	(1,550)
Net cash used in financing activities			(1,185)	(1,550)
Effect of exchange rate changes on cash			3	1
Net increase (decrease) in cash			24	(94)
Cash at beginning of year			141	225
Cash at end of period	165	131	165	131
Income taxes paid (received)			493	536
Interest paid			40	40
Reportable Legal Entities [Member] | Other Subsidiaries [Member]
Consolidating Statement of Cash Flows
Net income	34	213	340	621
Net adjustments to reconcile net income to net cash provided by operating activities			508	92
Net cash provided by operating activities			848	713
Proceeds from maturities of fixed maturities			1,618	1,788
Proceeds from sales of investments, fixed maturities			397	405
Proceeds from sales of investments, equity securities			202	32
Proceeds from sales of investments, real estate investments			23	69
Proceeds from sales of investments, other investments			190	170
Purchases of investments, fixed maturities			(2,493)	(2,978)
Purchases of investments, equity securities			(65)	(29)
Purchases of investments, real estate investments			(40)	(29)
Purchases of investments, other investments			(87)	(94)
Net (purchases) sales of short-term securities			(230)	366
Securities transactions in course of settlement			103	86
Acquisition, net of cash acquired			25
Other investing activities			5	(4)
Net cash used in investing activities			(352)	(218)
Dividends paid to parent company			(454)	(506)
Net cash used in financing activities			(454)	(506)
Effect of exchange rate changes on cash			8	(6)
Net increase (decrease) in cash			50	(17)
Cash at beginning of year			164	153
Cash at end of period	214	136	214	136
Income taxes paid (received)			174	206
Reportable Legal Entities [Member] | TRV [Member]
Consolidating Statement of Cash Flows
Net income	302	716	1,514	2,071
Net adjustments to reconcile net income to net cash provided by operating activities			285	127
Net cash provided by operating activities			1,799	2,198
Proceeds from maturities of fixed maturities			2	6
Proceeds from sales of investments, fixed maturities				2
Proceeds from sales of investments, equity securities			120
Purchases of investments, fixed maturities			(4)	(10)
Purchases of investments, equity securities			(123)	(2)
Net (purchases) sales of short-term securities			(272)	(162)
Securities transactions in course of settlement			1	3
Acquisition, net of cash acquired			(477)
Net cash used in investing activities			(753)	(163)
Treasury stock acquired - share repurchase authorization			(1,028)	(1,650)
Treasury stock acquired - net employee share-based compensation			(61)	(71)
Dividends paid to shareholders			(589)	(569)
Payment of debt			(207)	(400)
Issuance of debt			689	491
Issuance of common stock - employee share options			148	164
Net cash used in financing activities			(1,048)	(2,035)
Net increase (decrease) in cash			(2)
Cash at beginning of year			2	2
Cash at end of period		2		2
Income taxes paid (received)			(200)	(94)
Interest paid			177	183
Eliminations [Member]
Consolidating Statement of Cash Flows
Net income	$ (338)	$ (751)	(1,590)	(2,186)
Net adjustments to reconcile net income to net cash provided by operating activities			(49)	130
Net cash provided by operating activities			(1,639)	(2,056)
Proceeds from sales of investments, other investments			(13)
Acquisition, net of cash acquired			13
Dividends paid to parent company			1,639	2,056
Net cash used in financing activities			$ 1,639	$ 2,056