Loans and Allowance for Loan Losses - LTV Ratios (Details) - Consumer - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 40,267	$ 37,636
Percentage of total	100.00%	100.00%
Less than or Equal to 80 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 38,570	$ 36,524
Percentage of total	96.00%	97.00%
Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 1,582	$ 1,019
Percentage of total	4.00%	3.00%
Greater than or Equal to 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 16	$ 28
Percentage of total	0.00%	0.00%
No LTV Available
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 99	$ 65
Percentage of total	0.00%	0.00%
Residential mortgage
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 38,044	$ 35,279
Residential mortgage | Less than or Equal to 80 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	36,604	34,472
Residential mortgage | Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	1,361	771
Residential mortgage | Greater than or Equal to 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	4	4
Residential mortgage | No LTV Available
Credit quality of consumer loans
Loans categorized by LTV ratio	75	32
Home Equity loans
Credit quality of consumer loans
Loans categorized by LTV ratio	2,223	2,357
Home Equity loans | Less than or Equal to 80 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	1,966	2,052
Home Equity loans | Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	221	248
Home Equity loans | Greater than or Equal to 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio	12	24
Home Equity loans | No LTV Available
Credit quality of consumer loans
Loans categorized by LTV ratio	$ 24	$ 33