Debt - Summary of Retail Deposits (Details) - Germany [Member] - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Outstanding Balance
Overnight deposits	$ 654	$ 555
Term deposits - 12 months	444	337
Term deposits - 24 months	192	123
Term deposits - 36 months	309	245
Total deposits	$ 1,599	$ 1,260
Weighted Average Interest Rate
Overnight deposits (percent)	0.85%	1.00%
Term deposits -12 months (percent)	1.27%	1.32%
Term deposits - 24 months (percent)	1.38%	1.44%
Term deposits - 36 months (percent)	1.60%	1.65%
Total deposits (percent)	1.18%	1.25%