Segments - Reconciliation of Gross Margin to Consolidated Income (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Segment Reporting Information [Line Items]
Add: other operating revenues	$ 4,646	$ 4,904
Less: other operating expenses	(4,424)	(4,822)
Operating income	222	82
Other expenses (income), net	43	(49)
Income before income tax expense	179	131
Operating Segments
Segment Reporting Information [Line Items]
Gross margin	615	546
Operating Segments | Health Plans
Segment Reporting Information [Line Items]
Gross margin	601	537
Add: other operating revenues	4,509	4,771
Operating Segments | Molina Medicaid Solutions
Segment Reporting Information [Line Items]
Gross margin	8	4
Add: other operating revenues	51	46
Operating Segments | Other
Segment Reporting Information [Line Items]
Gross margin	6	5
Add: other operating revenues	86	87
Other operating
Segment Reporting Information [Line Items]
Add: other operating revenues	189	125
Less: other operating expenses	$ (582)	$ (589)