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Basis of Presentation (Details) member in Millions		1 Months Ended		3 Months Ended			9 Months Ended		12 Months Ended
Basis of Presentation (Details) member in Millions	Aug. 01, 2016 USD ($)	Aug. 31, 2017	Jun. 30, 2017	Sep. 30, 2017 USD ($) member State	Jun. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($) member State Segment	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Mar. 31, 2017 USD ($)
Basis Of Presentation [Line Items]
Number of reportable segments (in segment) \| Segment							3
Goodwill impairment losses				$ 129,000,000	$ 61,000,000				$ 0
Impairment losses				$ 129,000,000		$ 0	$ 201,000,000	$ 0
Today's Options of New York, Inc. \| New York
Basis Of Presentation [Line Items]
Final purchase price of business acquisition	$ 38,000,000
Health Plans
Basis Of Presentation [Line Items]
Number of states in which entity operates (in state) \| State				12			12
Number of members eligible for the health care programs, approximately (in member) \| member				4.5			4.5
Minimum contract terms							3 years
Maximum contract terms							4 years
Goodwill impairment losses				$ 0	0
Impairment losses				0		$ 0	$ 0	$ 0
Medicare Acquisition terminated
Basis Of Presentation [Line Items]
Gain recognized on contract termination										$ 75,000,000
Molina Healthcare of Illinois, Inc.
Basis Of Presentation [Line Items]
Services contract term		4 years
Services contract renewal term		4 years
Mississippi Coordinated Access Network
Basis Of Presentation [Line Items]
Services contract renewal term			2 years
Molina Medicaid Solutions \| Subsidiaries
Basis Of Presentation [Line Items]
Goodwill impairment losses				28,000,000
Pathways \| Subsidiaries
Basis Of Presentation [Line Items]
Goodwill impairment losses				$ 101,000,000	59,000,000
Impairment losses					$ 72,000,000