Consolidated Statement of Income - USD ($) shares in Millions, $ in Millions		3 Months Ended								12 Months Ended
		Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues
Premiums										$ 27,059	$ 25,683	$ 24,534
Net investment income										2,474	2,397	2,302
Fee income										432	447	458
Net realized investment gains	[1]									114	216	68
Other revenues										203	159	263
Total revenues		$ 7,796	$ 7,723	$ 7,477	$ 7,286	$ 7,451	$ 7,325	$ 7,184	$ 6,942	30,282	28,902	27,625
Claims and expenses
Claims and claim adjustment expenses										18,291	17,467	15,070
Amortization of deferred acquisition costs										4,381	4,166	3,985
General and administrative expenses										4,297	4,170	4,154
Interest expense										352	369	363
Total claims and expenses		7,050	6,917	6,846	6,508	6,591	7,005	6,394	6,182	27,321	26,172	23,572
Income before income taxes		746	806	631	778	860	320	790	760	2,961	2,730	4,053
Income tax expense		125	97	107	109	309	27	195	143	438	674	1,039
Net income		$ 621	$ 709	$ 524	$ 669	$ 551	$ 293	$ 595	$ 617	$ 2,523	$ 2,056	$ 3,014
Net income per share
Basic (in dollars per share)		$ 2.33	$ 2.65	$ 1.93	$ 2.45	$ 2.00	$ 1.06	$ 2.13	$ 2.19	$ 9.37	$ 7.39	$ 10.39
Diluted (in dollars per share)		$ 2.32	$ 2.62	$ 1.92	$ 2.42	$ 1.98	$ 1.05	$ 2.11	$ 2.17	$ 9.28	$ 7.33	$ 10.28
Weighted average number of common shares outstanding
Basic (in shares)										267.4	276.0	288.1
Diluted (in shares)										269.8	278.6	291.0

[1] Total other-than-temporary impairment (OTTI) losses were $(1) million, $(13) million and $(40) million for the years ended December 31, 2018, 2017 and 2016, respectively. Of total OTTI, credit losses of $(1) million, $(14) million and $(29) million for the years ended December 31, 2018, 2017 and 2016, respectively, were recognized in net realized investment gains. In addition, unrealized gains (losses) from other changes in total OTTI of $0 million, $1 million and $(11) million for the years ended December 31, 2018, 2017 and 2016, respectively, were recognized in other comprehensive income (loss) as part of changes in net unrealized gains (losses) on investment securities having credit losses recognized in the consolidated statement of income.