Investment Securities Securities by Credit Rating (Details) - USD ($) $ in Millions	Jun. 30, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	$ 59,700	$ 80,289
Debt Securities, Trading and Available-for-sale	77,143	100,442
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	222	209
Debt Securities, Trading and Available-for-sale	222	209
Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	377	370
Debt Securities, Trading and Available-for-sale	377	370
Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	712	976
Debt Securities, Trading and Available-for-sale	712	976
Securities Remeasured at Fair Value [Member] | Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading and Available-for-sale	712	976
BBB Rating [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	80	71
BBB Rating [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	59	69
BBB Rating [Member] | Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	99	67
BB Rating [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	26	21
BB Rating [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	30	10
BB Rating [Member] | Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	244	471
AAA Rating [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	0	0
AAA Rating [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	34	43
AAA Rating [Member] | Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	0	0
AA Rating [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	69	81
AA Rating [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	223	214
AA Rating [Member] | Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	0	0
A Rating [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	32	25
A Rating [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	31	34
A Rating [Member] | Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	0	13
B Rating [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	5	4
B Rating [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	0	0
B Rating [Member] | Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	251	308
Not Rated [Member] | Mortgage-backed Securities, Issued by Private Enterprises [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	10	7
Not Rated [Member] | Commercial Mortgage Backed Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	0	0
Not Rated [Member] | Credit Risk Transfer Securities [Member]
Debt Securities, Available-for-sale [Line Items]
Debt Securities, Trading	$ 118	$ 117