Stock Plans (Narrative) (Details) $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2016 USD ($) ShareBasedCompensationPlan $ / shares shares	Sep. 30, 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	5
Shares authorized for grant under the plans (in shares) | shares	20,000,000
Shares available for grant under the plan (in shares) | shares	6,460,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized during the period	$ 4	$ 6
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	$ 14	$ 13
Shares granted (in shares) | shares	5,627,000	2,814,000
Restricted Stock
Restricted stock granted	$ 23	$ 13
Restricted stock vested	15	15
Fair value of unvested restricted stock	$ 37	$ 34	$ 33
Restriced stock, grant date fair value per share | $ / shares	$ 5.24	$ 7.92	$ 5.93
Remaining unrecognized compensation cost associated with unvested restricted stock awards	$ 33
Weighted average period over which unvested restricted stock awards unrecognized compensation cost is expected to be recognized (in years)	2 years