Activity in the ALLL by segment (Detail) - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2019		Mar. 31, 2018		Dec. 31, 2018		Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses		$ 156		$ 38
Allowance for Loan and Lease Losses, Write-offs		(125)		(106)
Loan recoveries		28		27
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	(31)
Loans and Leases Receivable, Allowance		1,643		1,694		$ 1,615		$ 1,735
Unfunded commitments reserve		66	[2]	69	[3]	69	[2]	79	[3]
Provision for Other Credit Losses		(3)	[2]	(10)	[3]
Financing Receivable, Allowance for Credit Losses		1,709		1,763
Commercial Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses		84		(16)
Allowance for Loan and Lease Losses, Write-offs		(33)		(23)
Loan recoveries		5		6
Allowance for Loan and Lease Losses, Adjustments, Other		0
Loans and Leases Receivable, Allowance		1,136		1,068		1,080		1,101
Unfunded commitments reserve		66	[2]	69	[3]	69	[2]	79	[3]
Provision for Other Credit Losses		(3)	[2]	(10)	[3]
Financing Receivable, Allowance for Credit Losses		1,202		1,137
Consumer Portfolio Segment [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Provision for loan losses		72		54
Allowance for Loan and Lease Losses, Write-offs		(92)		(83)
Loan recoveries		23		21
Allowance for Loan and Lease Losses, Adjustments, Other	[1]	(31)
Loans and Leases Receivable, Allowance		507		626		$ 535		$ 634
Financing Receivable, Allowance for Credit Losses		$ 507		$ 626

[1] Represents the allowance for restructured loans that were transferred from LHFI to LHFS during the period and subsequently sold in the second quarter of 2019.

[2] The unfunded commitments reserve is recorded in Other liabilities in the Consolidated Balance Sheets.

[3] The unfunded commitments reserve is recorded in Other liabilities in the Consolidated Balance Sheets