Loans and Allowance for Credit Losses (Allowance for Loan Losses and Lending Commitments Rollforward) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Allowance for loan losses rollforward
Beginning balance	$ 224	$ 274
Recoveries		1
Provision (release)	19	22
Other	0
Ending balance	243	297
Inherent	238	230
Specific	5	67
Allowance for lending commitments rollforward
Beginning balance	198	190
Provision for (release of) lending commitments	7	3
Other	0
Ending balance	205	193
Inherent	204	191
Specific	1	2
Corporate
Allowance for loan losses rollforward
Beginning balance	126	195
Recoveries		1
Provision (release)	6	13
Other	(1)
Ending balance	131	209
Inherent	126	142
Specific	5	67
Allowance for lending commitments rollforward
Beginning balance	194	185
Provision for (release of) lending commitments	7	3
Other	0
Ending balance	201	188
Inherent	200	186
Specific	1	2
Consumer
Allowance for loan losses rollforward
Beginning balance	4	4
Recoveries		0
Provision (release)	0	0
Other	0
Ending balance	4	4
Inherent	4	4
Specific	0	0
Allowance for lending commitments rollforward
Beginning balance	1	1
Provision for (release of) lending commitments	0	0
Other	0
Ending balance	1	1
Inherent	1	1
Specific	0	0
Residential Real Estate
Allowance for loan losses rollforward
Beginning balance	24	20
Recoveries		0
Provision (release)	(1)	0
Other	0
Ending balance	23	20
Inherent	23	20
Specific	0	0
Allowance for lending commitments rollforward
Beginning balance	0	0
Provision for (release of) lending commitments	0	0
Other	0
Ending balance	0	0
Inherent	0	0
Specific	0	0
Wholesale Real Estate
Allowance for loan losses rollforward
Beginning balance	70	55
Recoveries		0
Provision (release)	14	9
Other	1
Ending balance	85	64
Inherent	85	64
Specific	0	0
Allowance for lending commitments rollforward
Beginning balance	3	4
Provision for (release of) lending commitments	0	0
Other	0
Ending balance	3	4
Inherent	3	4
Specific	$ 0	$ 0