Significant Credit Concentrations (Details) - USD ($) $ in Billions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Maximum Credit Exposure by Category
On-balance sheet	$ 36	$ 32
Individuals [Member]
Maximum Credit Exposure by Category
On-balance sheet	7	7
Financial Services [Member]
Maximum Credit Exposure by Category
On-balance sheet	1	2
Loans to affiliates and other
Maximum Credit Exposure by Category
On-balance sheet	15	11
Due from Affiliates [Member]
Maximum Credit Exposure by Category
On-balance sheet	0	1
Institutions [Member]
Maximum Credit Exposure by Category
On-balance sheet	$ 13	$ 11