Investments (Tables)

9 Months Ended

Sep. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Amortized Cost, Gross Unrealized Gains and Losses, Fair Values of Investments

The amortized cost, gross unrealized gains, gross unrealized losses, and fair values of our investments as of September 30, 2018 and December 31, 2017 are presented below:

	September 30, 2018
(in millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Asset-backed securities	$	35	$	—	$	—	$	35
Corporate bonds	86		—		—		86
U.S. government agencies and government- sponsored agencies	8		—		—		8
U.S. treasuries	34		—		—		34
Exchange traded fund	1		—		—		1
Other debt securities	10		—		—		10
Total	$	174	$	—	$	—	$	174

	December 31, 2017
(in millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
U.S. treasuries	$	37	$	—	$	—	$	37
Exchange traded fund	1		—		—		1
Total	$	38	$	—	$	—	$	38

Investments with a Continuous Unrealized Loss Position

Investments in a continuous unrealized loss position for less than 12 months and 12 months or more as of September 30, 2018 and December 31, 2017 are presented below.

	September 30, 2018
	Less than 12 months				12 months or more				Total
(in millions)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
Asset-backed securities	$	26	$	—	$	—	$	—	$	26	$	—
Corporate bonds	72		—		—		—		72		—
U.S. government agencies and government-sponsored agencies	7		—		—		—		7		—
U.S. treasuries	31		—		—		—		31		—
Exchange Traded Fund	1		—		—		—		1		—
Other debt securities	8		—		—		—		8		—
Total	$	145	$	—	$	—	$	—	$	145	$	—

	December 31, 2017
	Less than 12 months				12 months or more				Total
(in millions)	Fair Value		Unrealized Losses		Fair Value		Unrealized Losses		Fair Value		Unrealized Losses
U.S. treasuries	$	5	$	—	$	24	$	—	$	29	$	—
Total	$	5	$	—	$	24	$	—	$	29	$	—

Fair Value of Debt Investments by Contractual Maturity

The fair value of debt investments by contractual maturity (actual maturities may differ from contractual maturities because borrowers may have the right to prepay obligations with or without prepayment penalties) are shown below.

	September 30, 2018
(in millions)	One year or less		Over One Year Through Five Years		Over Five Years Through Ten Years		Over Ten Years		Fair Value
Asset-backed securities	$	3	$	29	$	3	$	—	$	35
Corporate bonds	32		54		—		—		86
U.S. government agencies and government-sponsored agencies	1		2		—		5		8
U.S. treasuries	7		27		—		—		34
Other debt securities	—		1		—		9		10
Total	$	43	$	113	$	3	$	14	$	173

	December 31, 2017
(in millions)	One year or less		Over One Year Through Five Years		Over Five Years Through Ten Years		Over Ten Years		Fair Value
U.S. treasuries	$	—	$	37	$	—	$	—	$	37
Total	$	—	$	37	$	—	$	—	$	37