Summary of Significant Accounting Policies and Nature of Operations - Schedule of Impact Resulted from ASU 2017-07 Adoption (Details) $ in Millions	3 Months Ended	6 Months Ended
Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($) segment	Jun. 30, 2019 USD ($)
Accounting Policies [Abstract]
Number of operating segments \| segment			2
Securities held to maturity transferred to securities available for sale			$ 0	$ 170
Salaries and employee benefits	$ 697	$ 696	1,373	1,381
Other	$ 95	$ 100	$ 222	$ 210

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

No definition available.

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration