Loans, Lending Commitments and Allowance for Credit Losses - Activity of Allowance for Loan Losses and Lending Commitments (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Allowance for loan losses rollforward
Beginning balance			$ 238	$ 224
Gross charge-offs			(1)	(4)
Recoveries				54
Net recoveries (charge-offs)				50
Provision (release)	$ 34	$ 1	68	(33)
Other			(8)	(10)
Ending balance	297	231	297	231
Inherent	279	226	279	226
Specific	18	5	18	5
Allowance for lending commitments rollforward
Beginning balance			203	198
Provision (release)	16	1	36	6
Other			(5)	(3)
Ending balance	234	201	234	201
Inherent	230	194	230	194
Specific	4	7	4	7
Corporate
Allowance for loan losses rollforward
Beginning balance			144	126
Gross charge-offs			0	(4)
Recoveries				54
Net recoveries (charge-offs)				50
Provision (release)			69	(39)
Other			(7)	(2)
Ending balance	206	135	206	135
Inherent	188	130	188	130
Specific	18	5	18	5
Allowance for lending commitments rollforward
Beginning balance			198	194
Provision (release)			34	5
Other			(4)	(2)
Ending balance	228	197	228	197
Inherent	224	190	224	190
Specific	4	7	4	7
Consumer
Allowance for loan losses rollforward
Beginning balance			7	4
Gross charge-offs			0	0
Recoveries				0
Net recoveries (charge-offs)				0
Provision (release)			0	1
Other			0	0
Ending balance	7	5	7	5
Inherent	7	5	7	5
Specific	0	0	0	0
Allowance for lending commitments rollforward
Beginning balance			2	1
Provision (release)			0	0
Other			(1)	0
Ending balance	1	1	1	1
Inherent	1	1	1	1
Specific	0	0	0	0
Residential real estate
Allowance for loan losses rollforward
Beginning balance			20	24
Gross charge-offs			(1)	0
Recoveries				0
Net recoveries (charge-offs)				0
Provision (release)			5	(4)
Other			0	0
Ending balance	24	20	24	20
Inherent	24	20	24	20
Specific	0	0	0	0
Allowance for lending commitments rollforward
Beginning balance			0	0
Provision (release)			0	0
Other			0	0
Ending balance	0	0	0	0
Inherent	0	0	0	0
Specific	0	0	0	0
Commercial real estate
Allowance for loan losses rollforward
Beginning balance			67	70
Gross charge-offs			0	0
Recoveries				0
Net recoveries (charge-offs)				0
Provision (release)			(6)	9
Other			(1)	(8)
Ending balance	60	71	60	71
Inherent	60	71	60	71
Specific	0	0	0	0
Allowance for lending commitments rollforward
Beginning balance			3	3
Provision (release)			2	1
Other			0	(1)
Ending balance	5	3	5	3
Inherent	5	3	5	3
Specific	$ 0	$ 0	$ 0	$ 0