D&C Licensing revenue decreased $218 million or 1%, due mainly to lower revenue from licenses of Windows and Office Consumer, as well as a decrease in royalty revenue, offset in part by increased Windows Phone revenue. Retail and non-OEM sales of Windows declined $304 million or 41%, due mainly to the launch of Windows 8 in the prior year. Windows OEM revenue declined $136 million or 1%, due to continued softness in the consumer PC market, offset in part by a 12% increase in OEM Pro revenue. Office Consumer revenue declined $243 million or 8%, reflecting the transition of customers to Office 365 Consumer as well as continued softness in the consumer PC market. The declines in Windows OEM and Office Consumer revenue were partially offset by benefits realized from ending our support for Windows XP in April 2014. Windows Phone revenue increased $822 million or 48%, due mainly to the recognition of $382 million revenue under our joint strategic initiatives with Nokia, which concluded in conjunction with the acquisition of NDS, as well as an increase in phone patent licensing revenue.
D&C Licensing gross margin increased $172 million or 1%, primarily due to a $390 million or 20% decrease in cost of revenue. D&C Licensing cost of revenue decreased, due mainly to a $411 million or 23% decline in traffic acquisition costs.