Shareholders' Equity And Net Income Per Share Other (Details) - USD ($)	3 Months Ended	11 Months Ended	12 Months Ended
	Mar. 31, 2017	Nov. 22, 2011	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shareholders' Equity and Net Income Per Share [Line Items]
Initial Offering Period		November 22, 2011
Reserve for Unsecured Creditors Litigation			$ 0	$ 300,000,000
Loss Contingency Accrual, Provision			10,000,000	300,000,000	$ 0
Unsecured Creditors Litigation
Shareholders' Equity and Net Income Per Share [Line Items]
Loss Contingency, Damages Sought, Value Per Unit in Excess of Benchmark				32.50
Loss Contingency, Damages Sought, Unit in Excess of Benchmark				67.50
Loss Contingency Accrual, Provision			$ 10,000,000
Unsecured Creditors Litigation | Litigation, Damages Benchmark, Fourth LLP Agreement
Shareholders' Equity and Net Income Per Share [Line Items]
Cumulative Distributions Threshold				7,200,000,000
Loss Contingency Accrual, Provision	$ 27,000,000
Other income (expense), net | Unsecured Creditors Litigation | Judicial Ruling
Shareholders' Equity and Net Income Per Share [Line Items]
Loss Contingency Accrual, Provision				$ 300,000,000