Valuation of Debt and Equity Investments and Certain Liabilities (Tables)

12 Months Ended

Dec. 31, 2017

Fair Value Disclosures [Abstract]

Investments

Details of our investments are as follows:

	December 31, 2017						December 31, 2016
	Cash and Cash		Short-Term		Long-Term		Cash and Cash		Short-Term		Long-Term
	Equivalents		Investments		Investments		Equivalents		Investments		Investments
Measured at fair value:
Available-for-sale securities:
Money market funds	$	525	$	—	$	—	$	346	$	—	$	—
Corporate obligations		172		698		—		107		544		—
U.S. government agency and    Treasury securities		700		2,115		—		490		1,792		—
Trading securities:
Mutual funds		—		—		236		—		—		201
Total		1,397		2,813		236		943		2,336		201
Other measurement basis:
Equity-method investments		—		—		26		—		—		25
Cost-method investments		—		—		6		—		—		9
Cash on hand		259		—		—		211		—		—
Total	$	1,656	$	2,813	$	268	$	1,154	$	2,336	$	235

Assets and Liabilities Accounted for at Fair Value

The following are our assets and liabilities that were accounted for at fair value on a recurring basis. These tables do not include cash on hand, assets held by our postretirement plans, or assets and liabilities that are measured at historical cost or any basis other than fair value.

	December 31, 2017						December 31, 2016
	Level 1		Level 2		Total		Level 1		Level 2		Total
Assets:
Money market funds	$	525	$	—	$	525	$	346	$	—	$	346
Corporate obligations		—		870		870		—		651		651
U.S. government agency and    Treasury securities		2,765		50		2,815		2,042		240		2,282
Mutual funds		236		—		236		201		—		201
Total assets	$	3,526	$	920	$	4,446	$	2,589	$	891	$	3,480
Liabilities:
Deferred compensation	$	255	$	—	$	255	$	218	$	—	$	218
Total liabilities	$	255	$	—	$	255	$	218	$	—	$	218