. the 2017 credit facility provides back-up liquidity to fund ongoing working capital for general corporate purposes and various investment opportunities . at december 31 , 2017 , the company had no amount outstanding under the 2017 credit facility . commercial paper program . the company can issue unsecured commercial paper notes ( the 201ccp notes 201d ) on a private-placement basis up to a maximum aggregate amount outstanding at any time of $ 4.0 billion