Income Taxes Operating Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
UK
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	$ 325	$ 449
Capital Loss Carryforwards	294	360
U.S. Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	196	8
U.S. State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	474	443
Other
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	350	245
Capital Loss Carryforwards	$ 218	$ 206