Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ 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									$ 201,159	$ 184,840	$ 157,107
Operating costs									185,950	171,910	146,086
Earnings from operations									15,209	12,930	11,021
Net earnings									10,823	7,073	5,868
Net earnings attributable to UnitedHealth Group common shareholders									$ 10,558	$ 7,017	$ 5,813
Net earnings per share attributable to UnitedHealth Group common stockholders:
Basic									$ 10.95	$ 7.37	$ 6.10
Diluted									$ 10.72	$ 7.25	$ 6.01
Quarterly Financial Data (Unaudited) [Member]
Revenues	$ 52,061	$ 50,322	$ 50,053	$ 48,723	$ 47,535	$ 46,293	$ 46,485	$ 44,527
Operating costs	48,084	46,234	46,322	45,310	44,348	42,713	43,282	41,567
Earnings from operations	3,977	4,088	3,731	3,413	3,187	3,580	3,203	2,960
Net earnings	3,721	2,561	2,350	2,191	1,708	1,978	1,760	1,627
Net earnings attributable to UnitedHealth Group common shareholders	$ 3,617	$ 2,485	$ 2,284	$ 2,172	$ 1,684	$ 1,968	$ 1,754	$ 1,611
Net earnings per share attributable to UnitedHealth Group common stockholders:
Basic	$ 3.73	$ 2.57	$ 2.37	$ 2.28	$ 1.77	$ 2.07	$ 1.84	$ 1.69
Diluted	$ 3.65	$ 2.51	$ 2.32	$ 2.23	$ 1.74	$ 2.03	$ 1.81	$ 1.67