Derivatives (Offsetting Derivative Financial Instruments) (Detail) - USD ($) $ in Millions	Sep. 30, 2018		Dec. 31, 2017
Derivative Fair Value Gross Amount Assets Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	$ 984		$ 823
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	306		409
Derivative, Collateral, Obligation to Return Cash	(227)		(341)
Derivative Fair Value Gross Amount Liabilities Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	913		602
Derivative Fair Value Amount Offset Against Collateral Net	490		365
Assets [Member]
Derivative Fair Value Gross Amount Assets Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	977	[1]	815	[2]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(287)		(213)
Derivative, Collateral, Obligation to Return Cash	(260)	[3]	(362)	[4]
Derivative, Fair Value, Amount Offset Against Collateral, Net	430		240
Liability
Derivative Fair Value Gross Amount Liabilities Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	913	[1]	602	[2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(287)		(213)
Derivative, Collateral, Right to Reclaim Cash	(232)	[3]	(155)	[4]
Derivative Fair Value Amount Offset Against Collateral Net	394		234
Derivative | Assets [Member]
Derivative Fair Value Gross Amount Assets Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	977	[1]	815	[2]
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	(287)		(213)
Derivative, Collateral, Obligation to Return Cash	(260)	[3]	(362)	[4]
Derivative, Fair Value, Amount Offset Against Collateral, Net	430		240
Derivative | Liability
Derivative Fair Value Gross Amount Liabilities Not Offset Against Collateral Net
Gross amount recognized in the balance sheet	913	[1]	602	[2]
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	(287)		(213)
Derivative, Collateral, Right to Reclaim Cash	(232)	[3]	(155)	[4]
Derivative Fair Value Amount Offset Against Collateral Net	$ 394		$ 234

[1] Amount does not includ e IRLCs because these instruments are not subject to master netting or similar arrangements

[2] Amount does not include IRLCs because these instruments are not subject to master netting or similar arrangements .

[3] Amount of collateral received as an offset to asset positions or pledged as an offset to liability positions. Collateral values in excess of related derivative amounts recognized in the Condensed Consolidated Balance Sheets were excluded from this table.

[4] Amount of collateral received as an offset to asset positions or pledged as an offset to liability positions. Collateral values in excess of related derivative amounts recognized in the Condensed Consolidated Balance Sheets were excluded from this table.