Investments and Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2015

Investments, Debt and Equity Securities [Abstract]

Aggregate Market Value and Unrealized Losses of Investment

The following table shows the number, aggregate market value and unrealized losses (in millions) of investments with market values that were less than amortized cost as of December 31, 2014. These lower market values are primarily caused by fluctuations in interest rates and credit spreads. All remaining investments and marketable securities have been sold during 2015.

	Unrealized Loss < 12 months					Unrealized Loss > 12 months
	Number of investments	Aggregate Market Value		Unrealized Losses		Number of investments	Aggregate Market Value		Unrealized Losses
Government securities	—	$	—	$	—	1	$	8	$	—
State and municipal bonds	—	—		—		2	1		—
Corporate Securities	1	1		—		11	3		—
Other	—	—		—		1	—		—
Total	1	$	1	$	—	15	$	12	$	—

Schedule of Realized Gains on the Sales of Available-For-Sale Securities

Using the specific identification method, the proceeds and realized gains on the sales of available-for-sale securities were as follows (in millions):

	Year Ended December 31,
		2015		2014			2013
Proceeds		$	25	$	644		$	337
Realized gains		—		1			1
Realized losses		—		(1		)	—
Net realized gains included in other comprehensive income (loss) as of the end of the prior year		—		—			—