Loans and Allowance for Loan Losses - Loans in Consumer Portfolio Segment Based on Refreshed LTV ratios (Details) - USD ($) $ in Millions		3 Months Ended	12 Months Ended
		Mar. 31, 2019	Dec. 31, 2018
Consumer Loans
Credit quality of consumer loans
Percentage of total loans categorized by LTV ratio		100.00%	100.00%
Consumer
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 40,236	$ 40,267
Consumer | Less than or Equal to 80 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		37,773	38,570
Consumer | Greater than 80 and Less than 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		2,345	1,582
Consumer | Greater than or Equal to 100 Percent
Credit quality of consumer loans
Loans categorized by LTV ratio		21	16
Consumer | No LTV Available
Credit quality of consumer loans
Loans categorized by LTV ratio	[1]	97	99
Consumer | Residential mortgage
Credit quality of consumer loans
Loans categorized by LTV ratio		38,046	38,044
Consumer | Home equity loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 2,190	$ 2,223
Less than or Equal to 80 Percent | Consumer Loans
Credit quality of consumer loans
Percentage of total loans categorized by LTV ratio		94.00%	96.00%
Less than or Equal to 80 Percent | Home Equity Line of Credit [Member] | Consumer Loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 1,914	$ 1,966
Less than or Equal to 80 Percent | Residential mortgage | Consumer Loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 35,859	$ 36,604
Greater than 80 and Less than 100 Percent | Consumer Loans
Credit quality of consumer loans
Percentage of total loans categorized by LTV ratio		6.00%	4.00%
Greater than 80 and Less than 100 Percent | Home Equity Line of Credit [Member] | Consumer Loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 239	$ 221
Greater than 80 and Less than 100 Percent | Residential mortgage | Consumer Loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 2,106	$ 1,361
Greater than or Equal to 100 Percent | Consumer Loans
Credit quality of consumer loans
Percentage of total loans categorized by LTV ratio		0.00%	0.00%
Greater than or Equal to 100 Percent | Home Equity Line of Credit [Member] | Consumer Loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 13	$ 12
Greater than or Equal to 100 Percent | Residential mortgage | Consumer Loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 8	$ 4
No LTV Available | Consumer Loans
Credit quality of consumer loans
Percentage of total loans categorized by LTV ratio		0.00%	0.00%
No LTV Available | Home Equity Line of Credit [Member] | Consumer Loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 24	$ 24
No LTV Available | Residential mortgage | Consumer Loans
Credit quality of consumer loans
Loans categorized by LTV ratio		$ 73	$ 75

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