Loans and Allowance for Loan Losses - Loans in Consumer Portfolio Segment Based on Refreshed LTV ratios (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018
Consumer
Credit quality of consumer loans
Percentage of total	100.00%	100.00%
Consumer | Less than or Equal to 80 Percent
Credit quality of consumer loans
Percentage of total	95.00%	96.00%
Consumer | Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Percentage of total	5.00%	4.00%
Consumer | Greater than or Equal to 100 Percent
Credit quality of consumer loans
Percentage of total	0.00%	0.00%
Consumer | No LTV Available
Credit quality of consumer loans
Percentage of total	0.00%	0.00%
Consumer | residential mortgage and home equity [Member] | Less than or Equal to 80 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 35,893	$ 38,570
Consumer | residential mortgage and home equity [Member] | Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	1,689	1,582
Consumer | residential mortgage and home equity [Member] | Greater than or Equal to 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	12	16
Consumer | residential mortgage and home equity [Member] | No LTV Available
Credit quality of consumer loans
Loans categorized by LTV ratio	43	99
Consumer Portfolio Segment [Member]
Credit quality of consumer loans
Loans categorized by LTV ratio	37,637	40,267
Consumer Portfolio Segment [Member] | Residential mortgage
Credit quality of consumer loans
Loans categorized by LTV ratio	37,637	40,267
No LTV Available | Consumer Portfolio Segment [Member]
Credit quality of consumer loans
Loans categorized by LTV ratio	43	99
Greater than or Equal to 100 Percent | Consumer Portfolio Segment [Member]
Credit quality of consumer loans
Loans categorized by LTV ratio	12	16
Greater than 80 and Less than 100 Percent | Consumer Portfolio Segment [Member]
Credit quality of consumer loans
Loans categorized by LTV ratio	1,689	1,582
Less than or Equal to 80 Percent | Consumer Portfolio Segment [Member]
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 35,893	$ 38,570