Short-term and Long-term Investments, Restricted Deposits

Short-term and long-term investments and restricted deposits by investment type consist of the following ($ in millions):



	December 31, 2018									December 31, 2017
	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value		Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	362	$	1	$	(2	)	$	361	$	311	$	—	$	(2	)	$	309
Corporate securities	3,190		8		(52		)	3,146		2,208		12		(10		)	2,210
Restricted certificates of deposit	433		—		—			433		4		—		—			4
Restricted cash equivalents	8		—		—			8		17		—		—			17
Municipal securities	2,196		9		(18		)	2,187		2,085		12		(10		)	2,087
Asset-backed securities	686		1		(4		)	683		437		1		(1		)	437
Residential mortgage-backed securities	452		1		(9		)	444		337		1		(6		)	332
Commercial mortgage- backed securities	366		1		(6		)	361		272		1		(2		)	271
Private equity investments	387		—		—			387		176		—		—			176
Life insurance contracts	128		—		—			128		135		—		—			135
Total	$	8,208	$	21	$	(91	)	$	8,138	$	5,982	$	27	$	(31	)	$	5,978

The Company’s investments are debt securities classified as available-for-sale with the exception of life insurance contracts and certain private equity investments. The Company’s investment policies are designed to provide liquidity, preserve capital and maximize total return on invested assets with the focus on high credit quality securities. The Company limits the size of investment in any single issuer other than U.S. treasury securities and obligations of U.S. government corporations and agencies. As of December 31, 2018, 96% of the Company’s investments in rated securities carry an investment grade rating by nationally recognized statistical rating organizations. At December 31, 2018, the Company held certificates of deposit, life insurance contracts and private equity investments which did not carry a credit rating.

The Company's residential mortgage-backed securities are primarily issued by the Federal National Mortgage Association, Government National Mortgage Association or Federal Home Loan Mortgage Corporation, which carry implicit or explicit guarantees of the U.S. government. The Company's commercial mortgage-backed securities are primarily senior tranches with a weighted average rating of AA+ and a weighted average duration of 3.7 years at December 31, 2018.

In March 2018, the Company completed a 25% investment in RxAdvance, a full-service pharmacy benefit manager. In May 2018, the Company made an additional investment, bringing the total ownership to 28%. The investment is being accounted for using the equity method of accounting. In September 2018, the Company made an additional investment in RxAdvance in the form of convertible preferred stock.

The fair value of available-for-sale debt securities with gross unrealized losses by investment type and length of time that individual securities have been in a continuous unrealized loss position were as follows ($ in millions):



	December 31, 2018										December 31, 2017
	Less Than 12 Months					12 Months or More					Less Than 12 Months					12 Months or More
	Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value		Unrealized Losses			Fair Value
U.S. Treasury securities and obligations of U.S. government corporations and agencies	$	—		$	59	$	(2	)	$	202	$	(1	)	$	222	$	(1	)	$	79
Corporate securities	(27		)	1,389		(25		)	871		(6		)	1,044		(4		)	185
Municipal securities	(4		)	591		(14		)	806		(7		)	943		(3		)	175
Asset-backed securities	(2		)	318		(2		)	168		(1		)	228		—			28
Residential mortgage- backed securities	(1		)	61		(8		)	233		(1		)	109		(5		)	171
Commercial mortgage- backed securities	(2		)	137		(4		)	140		(1		)	112		(1		)	51
Total	$	(36	)	$	2,555	$	(55	)	$	2,420	$	(17	)	$	2,658	$	(14	)	$	689

As of December 31, 2018, the gross unrealized losses were generated from 3,096 positions out of a total of 4,190 positions. The change in fair value of fixed income securities is primarily a result of movement in interest rates subsequent to the purchase of the security.

For each security in an unrealized loss position, the Company assesses whether it intends to sell the security or if it is more likely than not the Company will be required to sell the security before recovery of the amortized cost basis for reasons such as liquidity, contractual or regulatory purposes. If the security meets this criterion, the decline in fair value is other-than-temporary and is recorded in earnings. The Company does not intend to sell these securities prior to maturity and it is not likely that the Company will be required to sell these securities prior to maturity; therefore, there is no indication of other-than-temporary impairment for these securities.

The contractual maturities of short-term and long-term investments and restricted deposits are as follows ($ in millions):



	December 31, 2018								December 31, 2017
	Investments				Restricted Deposits				Investments				Restricted Deposits
	Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value		Amortized Cost		Fair Value
One year or less	$	647	$	646	$	205	$	205	$	474	$	474	$	48	$	47
One year through five years	3,026		2,998		351		350		2,424		2,420		88		88
Five years through ten years	2,387		2,362		—		—		1,773		1,779		—		—
Greater than ten years	88		89		—		—		129		130		—		—
Asset-backed securities	1,504		1,488		—		—		1,046		1,040		—		—
Total	$	7,652	$	7,583	$	556	$	555	$	5,846	$	5,843	$	136	$	135

Actual maturities may differ from contractual maturities due to call or prepayment options. Private equity investments and life insurance contracts are included in the five years through ten years category. The Company has an option to redeem at amortized cost substantially all of the securities included in the greater than ten years category listed above.

The Company continuously monitors investments for other-than-temporary impairment. Certain investments have experienced a decline in fair value due to changes in credit quality, market interest rates and/or general economic conditions. The Company recognizes an impairment loss for private equity investments when evidence demonstrates that it is other-than-temporarily impaired. Evidence of a loss in value that is other-than-temporary may include the absence of an ability to recover the carrying amount of the investment or the inability of the investee to sustain a level of earnings that would justify the carrying amount of the investment.