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Employee Incentive Plans (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended	143 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay	10.00%
Defined Contribution Plan, Employer Matching Contribution, Percent of Match	50.00%
Defined Contribution Plan Vesting Period	6 years
401(k) plan contribution expense	$ 1	$ 1
Maximum shares of stock distributable under 2007 Stock Incentive Plan	30,000,000			30,000,000
Shares granted to external directors				25,636
Stock Incentive Plan Granted Shares Adjustment			640
2007 Stock Incentive Plan Compensation Expense	$ 16	$ 14
Estimated Future 2007 Stock Incentive Plan Compensation Expense	$ 36			$ 36
Post employment shares distribution				823,091
2007 Stock Incentive Plan (Shares)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting Percentage, description	• 10% on the first vesting date, which is on or about May 9 of each year; and• an additional 15% on each of the following six anniversaries of the first vesting, assuming continued employment with the Company and compliance with non-competition and other applicable covenants.
2007 Stock Incentive Plan (Shares) | External Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting period	5 years
2007 Stock Incentive Plan (Shares) | Commencing One Year After Grant Date [Member] | External Director [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting percentage per year	20.00%

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Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

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