Fair Value Measurements (Details 2) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis
Fair value of impaired loans	$ 341	$ 137

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

No definition available.

Name:	us-gaap_FairValueAssetsAndLiabilitiesMeasuredOnRecurringAndNonrecurringBasisLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration