FAIR VALUE (Tables)

3 Months Ended

Mar. 31, 2017

Fair Value Disclosures [Abstract]

Financial Assets Measured at Fair Value on Recurring Basis

The following table summarizes our fair value measurements at March 31, 2017 and December 31, 2016, 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)
March 31, 2017
Cash equivalents	$	8,034	$	8,034	$	—	$	—
Debt securities:
U.S. Treasury and other U.S. government corporations and agencies:
U.S. Treasury and agency obligations	821		—		821		—
Mortgage-backed securities	1,618		—		1,618		—
Tax-exempt municipal securities	3,369		—		3,366		3
Mortgage-backed securities:
Residential	8		—		8		—
Commercial	409		—		409		—
Asset-backed securities	132		—		132		—
Corporate debt securities	4,272		—		4,268		4
Total debt securities	10,629		—		10,622		7
Total invested assets	$	18,663	$	8,034	$	10,622	$	7
December 31, 2016
Cash equivalents	$	3,654	$	3,654	$	—	$	—
Debt securities:
U.S. Treasury and other U.S. government corporations and agencies:
U.S. Treasury and agency obligations	786		—		786		—
Mortgage-backed securities	1,637		—		1,637		—
Tax-exempt municipal securities	3,305		—		3,302		3
Mortgage-backed securities:
Residential	9		—		9		—
Commercial	304		—		304		—
Asset-backed securities	160		—		160		—
Corporate debt securities	3,597		—		3,593		4
Total debt securities	9,798		—		9,791		7
Total invested assets	$	13,452	$	3,654	$	9,791	$	7

Changes in Fair Value of Assets Measured Using Significant Unobservable Inputs

During the three months ended March 31, 2017 and 2016, the changes in the fair value of the assets measured using significant unobservable inputs (Level 3) were comprised of the following:

	For the three months ended March 31,
	2017						2016
	Private Placements		Auction Rate Securities		Total		Private Placements		Auction Rate Securities			Total
	(in millions)
Beginning balance at January 1	$	4	$	3	$	7	$	6	$	5		$	11
Settlements	—		—		—		—		(2		)	(2		)
Balance at March 31	$	4	$	3	$	7	$	6	$	3		$	9