Our investment securities portfolio consists of the following: U.S. Treasury securities, U.S. government-sponsored enterprise or agency (“Agency”) and non-agency residential mortgage-backed securities (“RMBS”), Agency commercial mortgage-backed securities (“CMBS”) and other securities. Agency securities include Government National Mortgage Association (“Ginnie Mae”) guaranteed securities, Federal National Mortgage Association (“Fannie Mae”) and Federal Home Loan Mortgage Corporation (“Freddie Mac”) issued securities. The carrying value of our investments in U.S. Treasury and Agency securities represented 96% of our total investment securities portfolio as of both September 30, 2020 and December 31, 2019.

In the first quarter of 2020, we adopted the CECL standard. For our purchased credit-deteriorated (“PCD”) securities, which are classified as available for sale, this adoption resulted in an increase of their amortized cost basis and related allowance for credit losses. The allowance for credit losses for these PCD securities is limited to the amount by which the amortized cost basis of the security exceeds its fair value. This limitation resulted in an increase of $11 million to our retained earnings with a corresponding decrease in AOCI at adoption.

We exclude accrued interest receivable from the amortized cost disclosed in this note. Our disclosures below reflect these adoption changes. Prior period presentation was not reclassified to conform to the current period presentation. See “Note 1—Summary of Significant Accounting Policies” for additional information.

The table below presents the amortized cost, gross unrealized gains and losses, and fair value of securities available for sale as of September 30, 2020 and December 31, 2019. Accrued interest receivable of $251 million as of September 30, 2020 is not included in the below table.


	September 30, 2020
(Dollars in millions)	Amortized Cost		Allowance for Credit Losses		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Investment securities available for sale:
U.S. Treasury securities	$	9,331	$	0	$	14	$	0	$	9,345
RMBS:
Agency	72,948		0		2,506		(88)		75,366
Non-agency	1,093		(3)		204		(1)		1,293
Total RMBS	74,041		(3)		2,710		(89)		76,659
Agency CMBS	10,953		0		490		(8)		11,435
Other securities(1)	2,410		0		4		0		2,414
Total investment securities available for sale	$	96,735	$	(3)	$	3,218	$	(97)	$	99,853


	December 31, 2019
(Dollars in millions)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses		Fair Value
Investment securities available for sale:
U.S. Treasury securities	$	4,122	$	6	$	(4)	$	4,124
RMBS:
Agency	62,003		1,120		(284)		62,839
Non-agency	1,235		266		(2)		1,499
Total RMBS	63,238		1,386		(286)		64,338
Agency CMBS	9,303		165		(42)		9,426
Other securities(1)	1,321		4		0		1,325
Total investment securities available for sale	$	77,984	$	1,561	$	(332)	$	79,213

(1)Includes $1.5 billion and $117 million of asset-backed securities as of September 30, 2020, and December 31, 2019, respectively. The remaining amount is primarily comprised of supranational bonds and foreign government bonds.

The table below provides the gross unrealized losses and fair value of our securities available for sale aggregated by major security type and the length of time that individual securities have been in a continuous unrealized loss position as of September 30, 2020 and December 31, 2019. The amounts as of September 30, 2020 only include securities available for sale without an allowance for credit losses.


	September 30, 2020
	Less than 12 Months				12 Months or Longer				Total
(Dollars in millions)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Investment securities available for sale without an allowance for credit losses:
U.S. Treasury securities	$	0	$	0	$	0	$	0	$	0	$	0
RMBS:
Agency	6,681		(51)		1,866		(37)		8,547		(88)
Non-agency	14		0		0		0		14		0
Total RMBS	6,695		(51)		1,866		(37)		8,561		(88)
Agency CMBS	916		(4)		257		(4)		1,173		(8)
Other securities(1)	442		0		3		0		445		0
Total investment securities available for sale in a gross unrealized loss position without an allowance for credit losses(2)	$	8,053	$	(55)	$	2,126	$	(41)	$	10,179	$	(96)


	December 31, 2019
	Less than 12 Months				12 Months or Longer				Total
(Dollars in millions)	Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses		Fair Value		Gross Unrealized Losses
Investment securities available for sale:
U.S. Treasury securities	$	2,647	$	(4)	$	0	$	0	$	2,647	$	(4)
RMBS:
Agency	10,494		(92)		10,567		(192)		21,061		(284)
Non-agency	35		(1)		16		(1)		51		(2)
Total RMBS	10,529		(93)		10,583		(193)		21,112		(286)
Agency CMBS	2,580		(23)		1,563		(19)		4,143		(42)
Other securities(1)	126		0		106		0		232		0
Total investment securities available for sale in a gross unrealized loss position	$	15,882	$	(120)	$	12,252	$	(212)	$	28,134	$	(332)

The table below summarizes, by major security type, the contractual maturities and weighted-average yields of our investment securities as of September 30, 2020. Because borrowers may have the right to call or prepay certain obligations, the expected maturities of our securities are likely to differ from the scheduled contractual maturities presented below. The weighted-average yield below represents the effective yield for the investment securities and is calculated based on the amortized cost of each security.


	September 30, 2020
(Dollars in millions)	Due in 1 Year or Less			Due > 1 Year through 5 Years			Due > 5 Years through 10 Years			Due > 10 Years			Total
Fair value of securities available for sale:
U.S. Treasury securities	$	101		$	9,244		$	0		$	0		$	9,345
RMBS(1):
Agency	0			73			1,073			74,220			75,366
Non-agency	0			0			0			1,293			1,293
Total RMBS	0			73			1,073			75,513			76,659
Agency CMBS(1)	52			2,766			5,242			3,375			11,435
Other securities	251			1,882			281			0			2,414
Total securities available for sale	$	404		$	13,965		$	6,596		$	78,888		$	99,853
Amortized cost of securities available for sale	$	402		$	13,901		$	6,334		$	76,098		$	96,735
Weighted-average yield for securities available for sale	1.44		%	0.82		%	1.93		%	2.37		%	2.11		%

For the three and nine months ended September 30, 2020, total proceeds from the sale of our securities were $668 million and $812 million, respectively, with gains of $25 million in both periods. For the three and nine months ended September 30, 2019, total proceeds from sale of our securities were $243 million and $4.2 billion, with gains of $5 million and $44 million, respectively.

We pledged investment securities totaling $11.5 billion and $14.0 billion as of September 30, 2020 and December 31, 2019, respectively. These securities are primarily pledged to secure Federal Home Loan Banks (“FHLB”) advances and Public Funds deposits, as well as for other purposes as required or permitted by law. We accepted pledges of securities with a fair value of approximately $1 million as of both September 30, 2020 and December 31, 2019, related to our derivative transactions.