Commitments And Contingencies Unsecured Creditors Litigation (Details) - USD ($)	1 Months Ended	3 Months Ended		12 Months Ended
	Jul. 31, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Loss Contingencies [Line Items]
Reserve for Unsecured Creditors Litigation				$ 0	$ 300,000,000
Loss Contingency Accrual, Provision				10,000,000	300,000,000	$ 0
Unsecured Creditors Litigation
Loss Contingencies [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
Litigation Settlement, Amount Awarded to Other Party		$ 310,000,000
Payments for Legal Settlements	$ 310,000,000
Judicial Ruling | Unsecured Creditors Litigation
Loss Contingencies [Line Items]
Per share loss contingency accrual provision					$ 1.10
Litigation, Damages Benchmark, Fourth LLP Agreement | Unsecured Creditors Litigation
Loss Contingencies [Line Items]
Cumulative Distributions Threshold					$ 7,200,000,000
Loss Contingency Accrual, Provision			$ 27,000,000
Other income (expense), net | Judicial Ruling | Unsecured Creditors Litigation
Loss Contingencies [Line Items]
Loss Contingency Accrual, Provision					$ 300,000,000