Stock Plans (Narrative) (Details) $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) ShareBasedCompensationPlan $ / shares shares	Jun. 30, 2018 USD ($) $ / shares shares	Dec. 31, 2018 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock-based compensation plan under which grants were made | ShareBasedCompensationPlan	7
Number of stock-based compensation plan under which grants were not made | ShareBasedCompensationPlan	6
EIP Plans [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under the plans (in shares) | shares	5,667,000
Shares available for grant under the plan (in shares) | shares	2,797,000
Performance Shares [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares authorized for grant under the plans (in shares) | shares			497,000
Expense recognized during the period | $	$ 1	$ 2
Shares outstanding | shares	436,000		497,000
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense recognized during the period | $	$ 5	$ 7
Shares granted (in shares) | shares	105,000	1,996,000
Shares outstanding | shares	1,244,000		1,858,000
Restricted Stock
Restricted stock granted, Aggregate fair value | $		$ 11
Restricted stock vested, fair value | $	$ 1
Fair value of unvested restricted stock | $	$ 2	$ 11	$ 4
Restriced stock, grant date fair value per share | $ / shares	$ 11.28	$ 8.30	$ 16.02
Remaining unrecognized compensation cost associated with unvested restricted stock awards | $	$ 10
Weighted average period over which unvested restricted stock awards unrecognized compensation cost is expected to be recognized (in years)	1 year