Basis of Presentation Basis of Presentation (Details) - Sep. 30, 2018 £ in Millions, $ in Millions	GBP (£)	USD ($)
United Kingdom, Pounds
Out-of-Period Adjustment, Gross | £	£ 40
United States of America, Dollars
Out-of-Period Adjustment, Gross		$ 53
Out-of-Period Adjustment, Net		$ 43