Stock Plans (Narrative) (Details) $ / shares in Units, $ in Millions	3 Months Ended
	Mar. 31, 2016 USD ($) ShareBasedCompensationPlan $ / shares shares	Mar. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2015 USD ($) $ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock-based compensation plan under which grants were made | ShareBasedCompensationPlan	6
Number of stock-based compensation plan under which grants were not made | ShareBasedCompensationPlan	4
Shares authorized for grant under the plans (in shares) | shares	22,541,000
Shares available for grant under the plan (in shares) | shares	8,002,500
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized during the period	$ 1	$ 2
Shares granted (in shares) | shares	1,669,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized during the period	$ 5	$ 4
Shares granted (in shares) | shares	4,617,000	2,763,000
Restricted Stock
Restricted stock granted	$ 26	$ 19
Restricted stock vested	20	22
Fair value of unvested restricted stock	$ 45	$ 51	$ 33
Restriced stock, grant date fair value per share | $ / shares	$ 5.21	$ 7.98	$ 5.93
Remaining unrecognized compensation cost associated with unvested restricted stock awards	$ 38
Weighted average period over which unvested restricted stock awards unrecognized compensation cost is expected to be recognized (in years)	2 years