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Debt And Other Credit Facilities (Consolidated amount of non-recourse project-finance debt of a VIE) (Details) £ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)	Dec. 31, 2015 GBP (£)	Dec. 31, 2014
Long-term Debt, Maturing in Years Four and Five [Abstract]
2016	$ 10
2017	10
2018	10
2019	11
2020	12
Beyond 2019	$ 8
Class A 3.5% Index Linked Bonds [Member]
Debt Instrument [Line Items]
Guaranteed secured bonds, percentage			3.50%
Class B 5.9% Fixed Rate Bonds [Member]
Debt Instrument [Line Items]
Guaranteed secured bonds, percentage	5.90%	5.90%
Minimum [Member]
Debt Instrument [Line Items]
Subordinated notes payable, interest rate	11.25%
Maximum [Member]
Debt Instrument [Line Items]
Subordinated notes payable, interest rate	16.00%
United Kingdom, Pounds \| Class A 3.5% Index Linked Bonds [Member]
Debt Instrument [Line Items]
Secured bonds \| £		£ 56.0
United Kingdom, Pounds \| Class B 5.9% Fixed Rate Bonds [Member]
Debt Instrument [Line Items]
Secured bonds \| £		£ 16.7
United States of America, Dollars \| Class A 3.5% Index Linked Bonds [Member]
Debt Instrument [Line Items]
Secured bonds	$ 79
United States of America, Dollars \| Class B 5.9% Fixed Rate Bonds [Member]
Debt Instrument [Line Items]
Secured bonds	$ 24