Loans and Allowance for Loan Losses - Loans in Consumer Portfolio Segment Based on Refreshed LTV ratios (Details) - Consumer - USD ($) $ in Millions		9 Months Ended	12 Months Ended
		Sep. 30, 2017	Dec. 31, 2016
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 36,243	$ 32,089
Percentage of total loans categorized by LTV ratio		100.00%	100.00%
Less than or Equal to 80 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 35,333	$ 30,707
Percentage of total loans categorized by LTV ratio		98.00%	96.00%
Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 809	$ 1,236
Percentage of total loans categorized by LTV ratio		2.00%	4.00%
Greater than or Equal to 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 35	$ 57
Percentage of total loans categorized by LTV ratio		0.00%	0.00%
No LTV Available
Credit quality of consumer loans
Loans categorized by LTV ratio	[1]	$ 66	$ 89
Percentage of total loans categorized by LTV ratio	[1]	0.00%	0.00%
Residential mortgage
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 33,859	$ 29,639
Residential mortgage | Less than or Equal to 80 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		33,242	28,547
Residential mortgage | Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		574	1,030
Residential mortgage | Greater than or Equal to 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		10	16
Residential mortgage | No LTV Available
Credit quality of consumer loans
Loans categorized by LTV ratio	[1]	33	46
Home equity loans
Credit quality of consumer loans
Loans categorized by LTV ratio		2,384	2,450
Home equity loans | Less than or Equal to 80 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		2,091	2,160
Home equity loans | Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		235	206
Home equity loans | Greater than or Equal to 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		25	41
Home equity loans | No LTV Available
Credit quality of consumer loans
Loans categorized by LTV ratio	[1]	$ 33	$ 43

[1] Represents loans for which management was not able to obtain refreshed property values.