Expected Loss to be Paid - Net Expected Loss to be Paid (Recovered) and Net Economic Loss Development (Benefit) by Accounting Model (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	$ 718	$ 1,191	$ 718	$ 1,191	$ 960	$ 1,183	$ 1,432	$ 1,303
Economic loss development after recoveries for R&W	25	0	(14)	(5)
Public Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	548	870	548	870	772	864	1,082	1,203
Economic loss development after recoveries for R&W	55	39	200	50
Public Finance [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	520	832	520	832	749	832	1,041	1,157
Economic loss development after recoveries for R&W	50	42	204	59
Public Finance [Member] | Non United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	28		28			32
Economic loss development after recoveries for R&W			(4)
RMBS [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	135	303	135	303	162	293	326	73
Economic loss development after recoveries for R&W	(40)	(40)	(223)	(52)
RMBS [Member] | First Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	164		164			243
Economic loss development after recoveries for R&W	27	13	77	(4)
RMBS [Member] | Second Lien [Member] | United States [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	29		29			50
Economic loss development after recoveries for R&W	13	27	146	56
Other structured finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	35	18	35	18	26	26	24	27
Economic loss development after recoveries for R&W	10	1	9	(3)
Structured Finance [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	170	321	170	321	$ 188	319	$ 350	$ 100
Economic loss development after recoveries for R&W	(30)	(39)	(214)	(55)
Insurance Contracts [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	662		662			1,110
Economic loss development after recoveries for R&W	17	1	5	(9)
FG VIEs and other [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	61		61			75
Economic loss development after recoveries for R&W	(2)	(3)	(26)	(7)
Credit derivatives [Member]
Schedule of Expected Losses to be Paid [Line Items]
Net expected loss to be paid after recoveries for R&W	(5)		(5)			$ (2)
Economic loss development after recoveries for R&W	$ 10	$ 2	$ 7	$ 11