Securities Available for Sale (Detail) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		$ 31,910	$ 30,913	[1]
Unrealized Gains		142	250	[1]
Unrealized Losses		610	216	[1]
Available-for-sale Securities	[2],[3]	31,442	30,947	[1]
US Treasury Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		4,277	4,361
Unrealized Gains		0	2
Unrealized Losses		66	32
Available-for-sale Securities		4,211	4,331
US Government Agencies Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		221	257
Unrealized Gains		2	3
Unrealized Losses		2	1
Available-for-sale Securities		221	259
US States and Political Subdivisions Debt Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		606	618
Unrealized Gains		4	7
Unrealized Losses		21	8
Available-for-sale Securities		589	617
Asset-backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost			6
Unrealized Gains			2
Unrealized Losses			0
Available-for-sale Securities			8
Other Debt Obligations [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		14	17
Unrealized Gains		0	0
Unrealized Losses		0	0
Available-for-sale Securities		14	17
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		2,688	2,121
Unrealized Gains		8	3
Unrealized Losses		69	38
Available-for-sale Securities		2,627	2,086
Commercial Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		943	862
Unrealized Gains		0	7
Unrealized Losses		27	3
Available-for-sale Securities		916	866
Residential Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost		23,161	22,616
Unrealized Gains		128	222
Unrealized Losses		425	134
Available-for-sale Securities		$ 22,864	22,704
Residential Mortgage Backed Securities [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Amortized Cost			55
Unrealized Gains			4
Unrealized Losses			0
Available-for-sale Securities			$ 59

[1] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities AFS to Other assets on the Consolidated Balance Sheets. Prior periods have been revised to conform to the current presentation for comparability. See Note 11, "Other Assets," for additional information.

[2] Beginning January 1, 2018, the Company reclassified equity securities previously presented in Securities available for sale to Other assets. Reclassifications have been made to previously reported amounts for comparability.

[3] Includes securities AFS pledged as collateral where counterparties have the right to sell or repledge the collateral of $222 million and $223 million at December?31, 2018 and December?31, 2017, respectively.