Consolidated Statements of Cash Flows - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net income		$ 2,056	$ 3,014	$ 3,439
Adjustments to reconcile net income to net cash provided by operating activities:
Net realized investment gains	[1]	(216)	(68)	(3)
Depreciation and amortization		813	826	818
Deferred federal income tax expense		337	110	117
Amortization of deferred acquisition costs		4,166	3,985	3,885
Equity in income from other investments		(397)	(232)	(218)
Premiums receivable		(394)	(286)	(185)
Reinsurance recoverables		16	610	272
Deferred acquisition costs		(4,257)	(4,061)	(3,920)
Claims and claim adjustment expense reserves		1,460	(257)	(1,075)
Unearned premium reserves		521	372	248
Other operating activities		(343)	189	56
Net cash provided by operating activities		3,762	4,202	3,434
Cash flows from investing activities
Proceeds from maturities of fixed maturities		8,750	8,975	11,116
Proceeds from sales of investments:
Fixed maturities		1,854	1,417	1,950
Equity securities		765	92	59
Real estate investments		23	69	31
Other investments		857	839	713
Purchases of investments:
Fixed maturities		(12,250)	(11,609)	(12,090)
Equity securities		(459)	(51)	(49)
Real estate investments		(59)	(48)	(123)
Other investments		(541)	(580)	(534)
Net purchases of short-term securities		(26)	(199)	(326)
Securities transactions in course of settlement		(47)	(21)	(113)
Acquisitions, net of cash acquired		(439)		(13)
Other investing activities		(244)	(344)	(304)
Net cash provided by (used in) investing activities		(1,816)	(1,460)	317
Cash flows from financing activities
Treasury stock acquired - share repurchase authorization		(1,378)	(2,400)	(3,150)
Treasury stock acquired - net employee share-based compensation		(62)	(72)	(74)
Dividends paid to shareholders		(785)	(757)	(739)
Payment of debt		(657)	(400)	(400)
Issuance of debt		789	491	392
Issuance of common stock - employee share options		173	332	183
Excess tax benefits from share-based payment arrangements				55
Net cash used in financing activities		(1,920)	(2,806)	(3,733)
Effect of exchange rate changes on cash		11	(9)	(12)
Net increase (decrease) in cash		37	(73)	6
Cash at beginning of year		307	380	374
Cash at end of year		344	307	380
Supplemental disclosure of cash flow information
Income taxes paid		514	892	1,207
Interest paid		$ 367	$ 358	$ 365

[1] Total other-than-temporary impairment (OTTI) losses were $(13) million, $(40) million and $(54) million for the years ended December 31, 2017, 2016 and 2015, respectively. Of total OTTI, credit losses of $(14) million, $(29) million and $(52) million for the years ended December 31, 2017, 2016 and 2015, respectively, were recognized in net realized investment gains. In addition, unrealized gains (losses) from other changes in total OTTI of $1 million, $(11) million and $(2) million for the years ended December 31, 2017, 2016 and 2015, respectively, were recognized in other comprehensive income (loss) as part of changes in net unrealized gains on investment securities having credit losses recognized in the consolidated statements of income.