Investments AFS by Contractual Maturity (Details) - USD ($) $ in Millions		Mar. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale [Line Items]
Amortized Cost of AFS	[1]	$ 16,427	$ 15,206
Available-for-sale (AFS) securities	[2]	16,175	15,495
Non Mortgage Backed Securities
Debt Securities, Available-for-sale [Line Items]
Due in 1 year or less - Amortized cost		3,290	2,309
Due in 1 year or less - Fair value		3,293	2,312
Due after 1 year through 5 years - Amortized cost		2,057	2,972
Due after 1 year through 5 years - Fair value		2,060	2,976
Amortized Cost of AFS		5,347	5,281
Available-for-sale (AFS) securities		5,353	5,288
Total MBS
Debt Securities, Available-for-sale [Line Items]
Amortized Cost of AFS	[1]	11,080	9,925
Available-for-sale (AFS) securities		$ 10,822	$ 10,207

[1] Amortized cost includes unpaid principal balance, unamortized premiums and discounts, net charge-offs, and valuation adjustments for hedging activities, and excludes accrued interest receivable of $51 and $58 at March 31, 2020, and December 31, 2019, respectively.

[2] At March 31, 2020, $643 of these securities were pledged as collateral that may be repledged. At December 31, 2019, $381 of these securities were pledged as collateral that may be repledged.