For the Years Ended December 31, | |||||||||||
(in millions) | 2013 | 2012 | 2011 | ||||||||
Research and development expense | $ | 153 | $ | 136 | $ | 128 | |||||
Advertising expense | $ | 7 | $ | 6 | $ | 5 | |||||
Interest and other debt expense, net: | |||||||||||
Interest expense | $ | 1,053 | $ | 1,128 | $ | 1,220 | |||||
Interest income | (4 | ) | (2 | ) | (4 | ) | |||||
$ | 1,049 | $ | 1,126 | $ | 1,216 | ||||||
Rent expense | $ | 49 | $ | 49 | $ | 63 | |||||