Segment Information - Reconciliation of Gross Margin to Consolidated Income (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Segment Reporting Information [Line Items]
Gross margin	$ 254	$ 454	$ 800	$ 874
Total revenue	4,999	4,359	9,903	8,702
Less: other operating expenses	(5,286)	(4,254)	(10,108)	(8,508)
Operating (loss) income	(287)	105	(205)	194
Other expenses (income), net	27	25	(22)	50
(Loss) income before income tax (benefit) expense	(314)	80	(183)	144
Health Plans
Segment Reporting Information [Line Items]
Gross margin	249	435	786	842
Total revenue	4,868	4,223	9,639	8,424
Molina Medicaid Solutions
Segment Reporting Information [Line Items]
Gross margin	4	5	8	11
Total revenue	47	46	93	98
Other
Segment Reporting Information [Line Items]
Gross margin	1	14	6	21
Total revenue	84	90	171	180
Operating Segments
Segment Reporting Information [Line Items]
Gross margin	254	454	800	874
Operating Segments | Health Plans
Segment Reporting Information [Line Items]
Gross margin	249	435	786	842
Operating Segments | Molina Medicaid Solutions
Segment Reporting Information [Line Items]
Gross margin	4	5	8	11
Operating Segments | Other
Segment Reporting Information [Line Items]
Gross margin	1	14	6	21
Other operating
Segment Reporting Information [Line Items]
Total revenue	130	195	255	403
Less: other operating expenses	$ (671)	$ (544)	$ (1,260)	$ (1,083)