Consolidated Statements Of Income - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues:
Premiums									$ 52,380	$ 53,021	$ 52,409
Services									982	969	1,406
Investment income									405	389	474
Total revenues	$ 13,189	$ 13,282	$ 13,534	$ 13,762	$ 12,878	$ 13,694	$ 14,007	$ 13,800	53,767	54,379	54,289
Operating expenses:
Benefits									43,496	45,007	44,269
Operating costs									6,567	7,173	7,295
Merger termination fee and related costs, net									(936)	104	23
Depreciation and amortization									378	354	355
Total operating expenses									49,505	52,638	51,942
Income (loss) from operations									4,262	1,741	2,347
Gain on sale of business									0	0	270
Interest expense									242	189	186
Income (loss) before income taxes	490	799	1,042	1,689	(486)	902	636	500	4,020	1,552	2,431
Provision for income taxes									1,572	938	1,155
Net income	$ 184	$ 499	$ 650	$ 1,115	$ (401)	$ 450	$ 311	$ 254	$ 2,448	$ 614	$ 1,276
Basic earnings per common share (in dollars per share)	$ 1.30	$ 3.46	$ 4.49	$ 7.54	$ (2.68)	$ 3.01	$ 2.08	$ 1.70	$ 16.94	$ 4.11	$ 8.54
Diluted earnings per common share (in dollars per share)	$ 1.29	$ 3.44	$ 4.46	$ 7.49	$ (2.68)	$ 2.98	$ 2.06	$ 1.68	$ 16.81	$ 4.07	$ 8.44