CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Nov. 30, 2014	Dec. 31, 2013
2 3/4 Percent Convertible Senior Notes [Member]
Financing activities:
Principal amount repurchased		$ 140
Convertible Senior Notes [Member] | 1 Percent Convertible Senior Notes [Member]
Adjustments to reconcile net loss to net cash provided by operating activities:
Interest rate on convertible senior notes	1.00%	1.00%
Convertible Senior Notes [Member] | 2 3/4 Percent Convertible Senior Notes [Member]
Adjustments to reconcile net loss to net cash provided by operating activities:
Interest rate on convertible senior notes	2.75%	2.75%		2.75%
Financing activities:
Principal amount repurchased			$ 140