Segments - Reconciliation of Gross Margin to Consolidated Income (Details) - USD ($) $ in Millions	3 Months Ended	9 Months Ended
Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Segment Reporting Information [Line Items]
Add: other operating revenues	$ 4,697	$ 5,031	$ 14,226	$ 14,934
Add: gain on sale of subsidiary	37	0	37	0
Total operating expenses	4,439	5,112	13,404	15,220
Operating income (loss)	295	(81)	859	(286)
Other expenses, net	36	32	116	10
Income (loss) before income tax expense (benefit)	259	(113)	743	(296)
Health Plans
Segment Reporting Information [Line Items]
Add: other operating revenues	4,565	4,899	13,826	14,538
Molina Medicaid Solutions
Segment Reporting Information [Line Items]
Add: other operating revenues	53	47	152	140
Other
Segment Reporting Information [Line Items]
Add: other operating revenues	79	85	248	256
Operating Segments
Segment Reporting Information [Line Items]
Gross margin	566	564	1,854	1,364
Operating Segments \| Health Plans
Segment Reporting Information [Line Items]
Gross margin	547	557	1,812	1,343
Operating Segments \| Molina Medicaid Solutions
Segment Reporting Information [Line Items]
Gross margin	14	5	26	13
Operating Segments \| Other
Segment Reporting Information [Line Items]
Gross margin	5	2	16	8
Other operating
Segment Reporting Information [Line Items]
Add: other operating revenues	230	124	661	379
Add: gain on sale of subsidiary	37	0	37	0
Total operating expenses	$ 538	$ 769	$ 1,693	$ 2,029

Total costs of sales and operating expenses for the period.

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