Segment Financial Information (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Statement [Line Items]
Premiums, revenues - unaffiliated customers	$ 44,084	$ 38,938
Products, revenues - unaffiliated customers	6,702	6,129
Services, revenues - unaffiliated customers	4,104	3,434
Investment and other income	298	222
Total revenues	55,188	48,723
Earnings from operations	4,053	3,413
Interest expense	(329)	(283)
Earnings before income taxes	3,724	3,130
Optum
Statement [Line Items]
Investment and other income	115	61
Total revenues	23,601	21,237
Earnings from operations	1,653	1,279
Interest expense	0	0
Earnings before income taxes	1,653	1,279
Unaffiliated Customers
Statement [Line Items]
Premiums, revenues - unaffiliated customers	44,084	38,938
Products, revenues - unaffiliated customers	6,702	6,129
Services, revenues - unaffiliated customers	4,104	3,434
Total revenues	54,890	48,501
Unaffiliated Customers | Optum
Statement [Line Items]
Premiums, revenues - unaffiliated customers	847	885
Products, revenues - unaffiliated customers	6,702	6,129
Services, revenues - unaffiliated customers	2,065	1,512
Total revenues	9,614	8,526
Affiliated Customers
Statement [Line Items]
Total revenues	0	0
Affiliated Customers | Optum
Statement [Line Items]
Total revenues	13,872	12,650
Operating Segments | UnitedHealthcare
Statement [Line Items]
Investment and other income	183	161
Total revenues	45,459	40,136
Earnings from operations	2,400	2,134
Interest expense	0	0
Earnings before income taxes	2,400	2,134
Operating Segments | OptumHealth
Statement [Line Items]
Investment and other income	106	56
Total revenues	5,759	4,733
Earnings from operations	488	332
Interest expense	0	0
Earnings before income taxes	488	332
Operating Segments | OptumInsight
Statement [Line Items]
Investment and other income	2	1
Total revenues	2,069	1,843
Earnings from operations	395	294
Interest expense	0	0
Earnings before income taxes	395	294
Operating Segments | OptumRx
Statement [Line Items]
Investment and other income	7	4
Total revenues	16,106	14,947
Earnings from operations	770	653
Interest expense	0	0
Earnings before income taxes	770	653
Operating Segments | Unaffiliated Customers | UnitedHealthcare
Statement [Line Items]
Premiums, revenues - unaffiliated customers	43,237	38,053
Products, revenues - unaffiliated customers	0	0
Services, revenues - unaffiliated customers	2,039	1,922
Total revenues	45,276	39,975
Operating Segments | Unaffiliated Customers | OptumHealth
Statement [Line Items]
Premiums, revenues - unaffiliated customers	847	885
Products, revenues - unaffiliated customers	12	12
Services, revenues - unaffiliated customers	1,188	721
Total revenues	2,047	1,618
Operating Segments | Unaffiliated Customers | OptumInsight
Statement [Line Items]
Premiums, revenues - unaffiliated customers	0	0
Products, revenues - unaffiliated customers	23	21
Services, revenues - unaffiliated customers	740	642
Total revenues	763	663
Operating Segments | Unaffiliated Customers | OptumRx
Statement [Line Items]
Premiums, revenues - unaffiliated customers	0	0
Products, revenues - unaffiliated customers	6,667	6,096
Services, revenues - unaffiliated customers	137	149
Total revenues	6,804	6,245
Operating Segments | Affiliated Customers | UnitedHealthcare
Statement [Line Items]
Total revenues	0	0
Operating Segments | Affiliated Customers | OptumHealth
Statement [Line Items]
Total revenues	3,606	3,059
Operating Segments | Affiliated Customers | OptumInsight
Statement [Line Items]
Total revenues	1,304	1,179
Operating Segments | Affiliated Customers | OptumRx
Statement [Line Items]
Total revenues	9,295	8,698
Optum Eliminations
Statement [Line Items]
Investment and other income	0	0
Total revenues	(333)	(286)
Earnings from operations	0	0
Interest expense	0	0
Earnings before income taxes	0	0
Optum Eliminations | Unaffiliated Customers
Statement [Line Items]
Premiums, revenues - unaffiliated customers	0	0
Products, revenues - unaffiliated customers	0	0
Services, revenues - unaffiliated customers	0	0
Total revenues	0	0
Optum Eliminations | Affiliated Customers
Statement [Line Items]
Total revenues	(333)	(286)
Corporate and Eliminations
Statement [Line Items]
Investment and other income	0	0
Total revenues	(13,872)	(12,650)
Earnings from operations	0	0
Interest expense	(329)	(283)
Earnings before income taxes	(329)	(283)
Corporate and Eliminations | Unaffiliated Customers
Statement [Line Items]
Premiums, revenues - unaffiliated customers	0	0
Products, revenues - unaffiliated customers	0	0
Services, revenues - unaffiliated customers	0	0
Total revenues	0	0
Corporate and Eliminations | Affiliated Customers
Statement [Line Items]
Total revenues	$ (13,872)	$ (12,650)