Consolidated Statement of Income - USD ($) shares in Millions, $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Revenues
Premiums									$ 29,044	$ 28,272	$ 27,059
Net investment income									2,227	2,468	2,474
Fee income									429	459	432
Net realized investment gains									2	113	114
Other revenues									279	269	203
Total revenues	$ 8,397	$ 8,275	$ 7,401	$ 7,908	$ 8,063	$ 8,013	$ 7,834	$ 7,671	31,981	31,581	30,282
Claims and expenses
Claims and claim adjustment expenses									19,123	19,133	18,291
Amortization of deferred acquisition costs									4,773	4,601	4,381
General and administrative expenses									4,509	4,365	4,297
Interest expense									339	344	352
Total claims and expenses	6,781	7,289	7,486	7,188	6,989	7,581	7,169	6,704	28,744	28,443	27,321
Income before income taxes	1,616	986	(85)	720	1,074	432	665	967	3,237	3,138	2,961
Income tax expense	306	159	(45)	120	201	36	108	171	540	516	438
Net income	$ 1,310	$ 827	$ (40)	$ 600	$ 873	$ 396	$ 557	$ 796	$ 2,697	$ 2,622	$ 2,523
Net income per share
Basic (in dollars per share)	$ 5.13	$ 3.24	$ (0.16)	$ 2.34	$ 3.37	$ 1.52	$ 2.11	$ 3.01	$ 10.56	$ 10.01	$ 9.37
Diluted (in dollars per share)	$ 5.10	$ 3.23	$ (0.16)	$ 2.33	$ 3.35	$ 1.50	$ 2.10	$ 2.99	$ 10.52	$ 9.92	$ 9.28
Weighted average number of common shares outstanding
Basic (in shares)									253.5	260.0	267.4
Diluted (in shares)									254.6	262.3	269.8