FAIR VALUE (Tables)

12 Months Ended

Dec. 31, 2015

Fair Value Disclosures [Abstract]

Financial Assets Measured at Fair Value on Recurring Basis

The following table summarizes our fair value measurements at December 31, 2015 and 2014, respectively, for financial assets measured at fair value on a recurring basis:

			Fair Value Measurements Using
	Fair Value		Quoted Prices in Active Markets (Level 1)		Other Observable Inputs (Level 2)		Unobservable Inputs (Level 3)
	(in millions)
December 31, 2015
Cash equivalents	$	2,229	$	2,229	$	—	$	—
Debt securities:
U.S. Treasury and other U.S. government corporations and agencies:
U.S. Treasury and agency obligations	332		—		332		—
Mortgage-backed securities	1,891		—		1,891		—
Tax-exempt municipal securities	2,668		—		2,663		5
Mortgage-backed securities:
Residential	13		—		13		—
Commercial	985		—		985		—
Asset-backed securities	263		—		263		—
Corporate debt securities	2,958		—		2,952		6
Total debt securities	9,110		—		9,099		11
Total invested assets	$	11,339	$	2,229	$	9,099	$	11
December 31, 2014
Cash equivalents	$	1,712	$	1,712	$	—	$	—
Debt securities:
U.S. Treasury and other U.S. government corporations and agencies:
U.S. Treasury and agency obligations	374		—		374		—
Mortgage-backed securities	1,498		—		1,498		—
Tax-exempt municipal securities	3,068		—		3,060		8
Mortgage-backed securities:
Residential	17		—		17		—
Commercial	843		—		843		—
Asset-backed securities	29		—		28		1
Corporate debt securities	3,718		—		3,695		23
Total debt securities	9,547		—		9,515		32
Total invested assets	$	11,259	$	1,712	$	9,515	$	32

Changes in Fair Value of Assets Measured Using Significant Unobservable Inputs

During the years ended December 31, 2015, 2014, and 2013, the changes in the fair value of the assets measured using significant unobservable inputs (Level 3) were comprised of the following:

	For the years ended December 31,
	2015									2014								2013
	Private Placements			Auction Rate Securities			Total			Private Placements		Auction Rate Securities			Total			Private Placements			Auction Rate Securities		Total
	(in millions)
Beginning balance at January 1	$	24		$	8		$	32		$	24	$	13		$	37		$	25		$	13	$	38
Total gains or losses:
Realized in earnings	(1		)	—			(1		)	—		—			—			—			—		—
Unrealized in other comprehensive income	—			—			—			—		—			—			—			—		—
Purchases	—			—			—			—		—			—			—			—		—
Sales	(17		)	(3		)	(20		)	—		(5		)	(5		)	—			—		—
Settlements	—			—			—			—		—			—			(1		)	—		(1		)
Balance at December 31	$	6		$	5		$	11		$	24	$	8		$	32		$	24		$	13	$	37