Loans and Allowance for Loan Losses - FICO Scores (Details) - Consumer - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	$ 38,685	$ 33,099
Percentage of total	100.00%	100.00%
720 and Above
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	$ 31,190	$ 25,970
Percentage of total	81.00%	78.00%
Below 720
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	$ 7,000	$ 6,574
Percentage of total	18.00%	20.00%
No FICO Available
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	$ 495	$ 555
Percentage of total	1.00%	2.00%
Residential mortgage
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	$ 35,279	$ 29,639
Residential mortgage | 720 and Above
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	28,786	23,598
Residential mortgage | Below 720
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	6,082	5,597
Residential mortgage | No FICO Available
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	411	444
Home equity and other consumer loans
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	3,406	3,460
Home equity and other consumer loans | 720 and Above
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	2,404	2,372
Home equity and other consumer loans | Below 720
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	918	977
Home equity and other consumer loans | No FICO Available
Credit quality of consumer loans
Loan balances, excluding loans serviced by third parties and loans covered by FDIC loss share agreements	$ 84	$ 111