Business Combinations - Consideration (Details) - USD ($) $ / shares in Units, shares in Thousands		12 Months Ended
	Dec. 06, 2019	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issued in business combination		$ 33,546,000,000	$ 0	$ 0
Issued in connection with equity awards, net		$ (15,000,000)	(6,000,000)	120,000,000
SunTrust Banks Inc.
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Shares Issued, Price Per Share	$ 54.24
Business Combination, Consideration Transferred, Equity Interests Issued and Issuable	$ 31,192,000,000
Payments to Acquire Businesses, Gross	1,000,000
Business Combination, Consideration Transferred	33,547,000,000
Issued in connection with equity awards, net	$ 309,000,000
Common Stock
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issued in business combinations (in shares)		575,067
Issued in business combination		$ 2,875,000,000
Issued in connection with equity awards, net		19,000,000	$ 23,000,000	$ 41,000,000
Common Stock | SunTrust Banks Inc.
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issued in business combinations (in shares)	575,067
Preferred Stock
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issued in business combination	$ 2,000,000,000.0	$ 2,045,000,000
Preferred Stock | SunTrust Banks Inc.
Business Acquisition, Equity Interests Issued or Issuable [Line Items]
Issued in business combination	$ 2,045,000,000