Investments (Tables)

3 Months Ended

Mar. 31, 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 March 31, 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	$	120
Due after one year through three years	374
Due after three years through five years	13
Due after five years	16
Total	$	523