Investments (Tables)

6 Months Ended

Jun. 30, 2018

Investments, Debt and Equity Securities [Abstract]

Schedule of maturities for short-term investments

The estimated fair values of short-term investments, which approximate cost at June 30, 2018, are shown below by contractual maturity. Actual maturities may differ from contractual maturities because issuers of the securities may have the right to retire our investments without prepayment penalties.

(in millions)	Total
Due in one year or less	$	189
Due after one year through three years	306
Due after three years through five years	10
Due after five years	15
Total	$	520