Summary of Significant Accounting Policies and Nature of Operations - Schedule of Impact Resulted from ASU 2017-07 Adoption (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Salaries and employee benefits	$ 678	$ 615	$ 1,348	$ 1,260
Other	$ 107	83	$ 199	173
As Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Salaries and employee benefits		586		1,201
Other		112		232
ASU 2017-07 | Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Salaries and employee benefits		29		59
Other		$ (29)		$ (59)