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Fair Value Of Financial Instruments (Changes In Level 3 Assets And Liabilities Measured At Fair Value On A Recurring Basis) (Detail) - Fair Value Inputs Level 3 [Member] - USD ($) $ in Millions		3 Months Ended
		Mar. 31, 2017	Mar. 31, 2016
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		$ 1,552	$ 1,834
Realized gains/(losses), assets		0	(1)
Unrealized gains/(losses) included in earnings, assets		1	(29)
Unrealized gains/(losses) included in OCI, assets		2	5
Foreign exchange recognized in OCI or earnings, assets		(3)	0
Purchases, assets		719	146
Issuances, assets		0	0
Settlements, assets		(111)	(99)
Sales, assets		0	0
Transfers into level 3, assets	[1]	8	5
Transfers out of level 3, assets	[1]	(3)	(11)
Ending balance, fair value assets		2,165	1,850
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets		(1)	(18)
Beginning balance, fair value liabilities		661	1,531
Realized gains/(losses), liabilities		31	14
Unrealized gains/(losses included in earnings, liabilities		57	(10)
Unrealized gains/(losses) included in OCI, liabilities		0	0
Foreign exchange recognized in OCI or earnings, liabilities		2	7
Purchases, liabilities		0	9
Issuances, liabilities		0	0
Settlements, liabilities		(50)	(92)
Sales, liabilities		0	0
Transfers into Level 3, liabilities	[1]	0	0
Transfers out of Level 3, liabilities	[1]	0	0
Ending balance, fair value liabilities		701	1,459
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities		59	0
Residential Prime Financing Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		916	1,185
Unrealized gains/(losses) included in earnings, assets		(4)	(14)
Settlements, assets		(68)	(56)
Ending balance, fair value assets		844	1,115
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets		(3)	(14)
Other Loans Receivable [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		150	107
Unrealized gains/(losses) included in earnings, assets		3
Purchases, assets		719	146
Ending balance, fair value assets		872	253
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets		3
Loan Repurchase Commitments [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		404	396
Unrealized gains/(losses) included in earnings, assets		5	3
Ending balance, fair value assets		409	399
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets		5	3
State and municipal bonds [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		0	41
Settlements, assets			(38)
Transfers into level 3, assets	[1]	1
Transfers out of level 3, assets		0
Ending balance, fair value assets		1	3
Foreign Government Debt [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		0	2
Purchases, assets		0
Settlements, assets		0
Ending balance, fair value assets		0	2
Corporate Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		2	7
Settlements, assets		0
Transfers out of level 3, assets		(2)	(6)
Ending balance, fair value assets		0	1
Corporate Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		0	11
Unrealized gains/(losses) included in earnings, assets			(5)
Transfers into level 3, assets		6
Transfers out of level 3, assets	[1]		(5)
Ending balance, fair value assets		6	1
Residential Mortgage Backed Non Agency [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		0
Unrealized gains/(losses) included in earnings, assets		0
Commercial Mortgage Backed Securities [Member]
Accounts Notes And Loans Receivable [Line Items]
Transfers into level 3, assets		0
Ending balance, fair value assets		0
Commercial Mortgage Backed Securities [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		0
Unrealized gains/(losses) included in earnings, assets		0
Transfers into level 3, assets		0	2
Ending balance, fair value assets		0	2
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets		0
Collateralized Debt Obligations [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		15	29
Unrealized gains/(losses) included in OCI, assets			0
Settlements, assets		(2)	(3)
Ending balance, fair value assets		13	26
Collateralized Debt Obligations [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		1	1
Ending balance, fair value assets		1	1
Other Asset Backed [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		44	38
Realized gains/(losses), assets			(1)
Unrealized gains/(losses) included in earnings, assets			(1)
Unrealized gains/(losses) included in OCI, assets		2	5
Settlements, assets		(41)	(2)
Transfers out of level 3, assets	[1]	0
Ending balance, fair value assets		5	39
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets			(1)
Other Asset Backed [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		1	6
Unrealized gains/(losses) included in earnings, assets			(6)
Transfers into level 3, assets		1	3
Transfers out of level 3, assets		(1)
Ending balance, fair value assets		1	3
Medium Term Notes [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value liabilities		101	161
Unrealized gains/(losses included in earnings, liabilities		1	(3)
Foreign exchange recognized in OCI or earnings, liabilities		2	7
Settlements, liabilities		0
Ending balance, fair value liabilities		104	165
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities		3	5
Credit Derivatives [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value liabilities		64	85
Realized gains/(losses), liabilities		31	14
Unrealized gains/(losses included in earnings, liabilities		22	14
Settlements, liabilities		(31)	(14)
Ending balance, fair value liabilities		86	99
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities		22	16
Other Derivative Liabilities [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value liabilities		20	18
Unrealized gains/(losses included in earnings, liabilities		0	1
Ending balance, fair value liabilities		20	19
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities		0	1
Variable Interest Entity Notes [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value liabilities		476	1,267
Unrealized gains/(losses included in earnings, liabilities		34	(22)
Purchases, liabilities			9
Settlements, liabilities		(19)	(78)
Ending balance, fair value liabilities		491	1,176
Change in unrealized gains/(losses) for the period included in earnings for liabilities still held, liabilities		34	(22)
Currency Derivatives [Member] | Variable Interest Entity Primary Beneficiary [Member]
Accounts Notes And Loans Receivable [Line Items]
Beginning balance, fair value assets		19	11
Unrealized gains/(losses) included in earnings, assets		(3)	(6)
Foreign exchange recognized in OCI or earnings, assets		(3)
Ending balance, fair value assets		13	5
Change in unrealized gains/(losses) for the period included in earnings for assets still held, assets		$ (6)	$ (6)
[1] Transferred in and out at the end of the period.

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