Other Assets (Details 2) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Components of other intangible assets
Gross Carrying Amount	$ 2,105	$ 1,885
Accumulated Amortization	(1,206)	(1,017)
Net Carrying Amount	899	868
Customer Relationships [Member]
Components of other intangible assets
Gross Carrying Amount	1,863	1,625
Accumulated Amortization	(1,073)	(895)
Net Carrying Amount	790	730
Other Contracts [Member]
Components of other intangible assets
Gross Carrying Amount	242	260
Accumulated Amortization	(133)	(122)
Net Carrying Amount	$ 109	$ 138