Loans, Lending Commitments and Allowance for Credit Losses - Impaired Loans and Lending Commitments before Allowance (Details) - USD ($) $ in Millions	Sep. 30, 2019	Dec. 31, 2018
Loans
With allowance	$ 232	$ 24
Without allowance	125	101
Total impaired loans	357	125
UPB	366	133
Lending commitments
With allowance	5	19
Without allowance	37	34
Total impaired lending commitments	42	53
Corporate
Loans
With allowance	232	24
Without allowance	28	32
Total impaired loans	260	56
UPB	267	63
Lending commitments
With allowance	5	19
Without allowance	37	34
Total impaired lending commitments	42	53
Consumer
Loans
With allowance	0	0
Without allowance	5	0
Total impaired loans	5	0
UPB	5	0
Lending commitments
With allowance	0	0
Without allowance	0	0
Total impaired lending commitments	0	0
Residential real estate
Loans
With allowance	0	0
Without allowance	92	69
Total impaired loans	92	69
UPB	94	70
Lending commitments
With allowance	0	0
Without allowance	0	0
Total impaired lending commitments	$ 0	$ 0