Investment Securities (Tables)
6 Months Ended 12 Months Ended
Jun. 30, 2016
Dec. 31, 2015
Investments, Debt and Equity Securities [Abstract]    
Schedule of Trading and Available-for-sale Securities  
As of December 31, 2015 and 2014, investment securities were comprised of the following:
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Fair Value
 
(Dollars in millions)
December 31, 2015
 
 
 
 
 
 
 
Available-for-sale securities
 
 
 
 
 
 
 
Agency - Commercial
$
766

 
$
3

 
$
(3
)
 
$
766

Agency - Residential
514

 
2

 
(2
)
 
514

Municipal obligations
14

 

 

 
14

Total available-for-sale securities
$
1,294

 
$
5

 
$
(5
)
 
$
1,294

Held-to-maturity securities
 
 
 
 
 
 
 
Agency - Commercial
$
634

 
$

 
$
(2
)
 
$
632

Agency - Residential
634

 

 
(4
)
 
630

Total held-to-maturity securities
$
1,268

 
$

 
$
(6
)
 
$
1,262

 
 
 
 
 
 
 
 
December 31, 2014
 
 
 
 
 
 
 
Available-for-sale securities
 
 
 
 
 
 
 
Agency - Commercial
$
541

 
$
1

 
$
(2
)
 
$
540

Agency - Residential
1,118

 
13

 
(1
)
 
1,130

Municipal obligations
2

 

 

 
2

Total available-for-sale securities
$
1,661

 
$
14

 
$
(3
)
 
$
1,672

Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value
The following table summarizes by duration the unrealized loss positions on investment securities: 
 
Unrealized Loss Position with
Duration 12 Months and Over
 
Unrealized Loss Position with
Duration Under 12 Months
  
Fair Value
 
Number of
Securities
 
Unrealized
Loss
 
Fair
Value
 
Number of
Securities
 
Unrealized
Loss
Type of Security
(Dollars in millions)
June 30, 2016
 
 
 
 
 
 
 
 
 
 
 
Available-for-sale securities
 
 
 
 
 
 
 
 
 
 
 
Agency - Commercial
$
7

 
1

 
$

 
$
13

 
2

 
$

Held-to-maturity securities
 
 
 
 
 
 
 
 
 
 
 
Agency - Commercial
$

 

 
$

 
$
57

 
4

 
$

December 31, 2015
 
 
 
 
 
 
 
 
 
 
 
Available-for-sale securities
 
 
 
 
 
 
 
 
 
 
 
Agency - Commercial
$

 

 
$

 
$
482

 
27

 
$
(3
)
Agency - Residential
$
8

 
2

 
$

 
$
224

 
15

 
$
(2
)
Held-to-maturity securities
 
 
 
 
 
 
 
 
 
 
 
Agency - Commercial
$

 

 
$

 
$
471

 
27

 
$
(2
)
Agency - Residential
$

 

 
$

 
$
547

 
50

 
$
(4
)
The following table summarizes by duration the unrealized loss positions on investment securities.
 
Unrealized Loss Position with Duration
12 Months and Over
 
Unrealized Loss Position with Duration
Under 12 Months
 
Fair
Value
 
Number of
Securities
 
Unrealized
Loss
 
Fair
Value
 
Number of
Securities
 
Unrealized
Loss
 
(Dollars in millions)
December 31, 2015
 
Available-for-sale securities
 
 
 
 
 
 
 
 
 
 
 
Agency - Commercial
$

 

 
$

 
$
482

 
27

 
$
(3
)
Agency - Residential
$
8

 
2
 
$

 
$
224

 
15

 
$
(2
)
Held-to-maturity securities
 
 
 
 
 
 
 
 
 
 
 
Agency - Commercial
$

 

 
$

 
$
471

 
27

 
$
(2
)
Agency - Residential
$

 
0

 
$

 
$
547

 
50

 
$
(4
)
December 31, 2014
 
 
 
 
 
 
 
 
 
 
 
Available-for-sale securities
 
 
 
 
 
 
 
 
 
 
 
Agency - Commercial
$
53

 
6

 
$

 
$
305

 
21

 
$
(2
)
Agency - Residential
$
98

 
10

 
$
(1
)
 
$
37

 
4

 
$

December 31, 2013
 
 
 
 
 
 
 
 
 
 
 
Available-for-sale securities
 
 
 
 
 
 
 
 
 
 
 
Agency - Commercial
$

 

 
$

 
$
326

 
19

 
$
(4
)
Agency - Residential
$

 

 
$

 
$
500

 
44

 
$
(6
)
Other than Temporary Impairment, Credit Losses Recognized in Earnings  
The following table shows the OTTI roll forward. 
 
For the Years Ended December 31,
 
2015
 
2014
 
2013
 
(Dollars in millions)
Beginning balance of amount related to credit losses
$

 
$

 
$
(3
)
Reductions for increases in cash flows expected to be collected that are recognized over the remaining life

 

 
1

Reductions for investment securities sold during the period (realized)

 

 
11

Additions for the amount related to the credit loss for which an OTTI impairment was not previously recognized

 

 
(9
)
Ending balance of amount related to credit losses
$

 
$

 
$

Schedule of Available-for-sale Securities, by Contractual Maturity Date
The amortized cost and estimated fair value of securities at June 30, 2016, are presented below by contractual maturity:
 
Investment Securities
Available-for-Sale
 
Investment Securities
Held-to-maturity
 
Amortized
Cost
 
Fair
Value
 
Weighted Average
Yield
 
Amortized
Cost
 
Fair
Value
 
Weighted Average
Yield
June 30, 2016
(Dollars in millions)
 
(Dollars in millions)
Due after one year through five years
$
18

 
$
18

 
3.97
%
 
$

 
$

 
%
Due after five years through 10 years
7

 
7

 
2.66
%
 
61

 
64

 
2.50
%
Due after 10 years
1,093

 
1,120

 
2.59
%
 
1,150

 
1,173

 
2.40
%
Total
$
1,118

 
$
1,145

 
 
 
$
1,211

 
$
1,237

 
 
The amortized cost and estimated fair value of investment securities at December 31, 2015, are presented below by contractual maturity. Expected maturities may differ from contractual maturities because issuers may have the right to call or prepay obligations.
 
Investment Securities
Available-for-Sale
 
Investment Securities
Held-to-Maturity
 
Amortized
Cost
Estimated Fair
Value
Weighted-Average
Yield
 
Amortized
Cost
Estimated Fair
Value
Weighted-Average
Yield
December 31, 2015
(Dollars in millions)
 
(Dollars in millions)
Due after five years through 10 years
$
14

$
14

4.47
%
 
$
58

$
57

2.48
%
Due after 10 years
1,280

1,280

2.54
%
 
1,210

1,205

2.41
%
Total
$
1,294

$
1,294

 
 
$
1,268

$
1,262

 
Marketable Securities
As of June 30, 2016 and December 31, 2015, investment securities were comprised of the following:
 
 
Amortized
Cost
 
Gross
Unrealized
Gains
 
Gross
Unrealized
Losses
 
Fair Value
 
 
(Dollars in millions)
June 30, 2016
 
 
 
 
 
 
 
 
Available-for-sale securities
 
 
 
 
 
 
 
 
Agency - Commercial
 
$
626

 
$
14

 
$

 
$
640

Agency - Residential
 
461

 
12

 

 
473

Municipal obligations
 
31

 
1

 

 
32

Total available-for-sale securities (1)
 
$
1,118

 
$
27

 
$

 
$
1,145

Held-to-maturity securities
 
 
 
 
 
 
 
 
Agency - Commercial
 
$
635

 
$
12

 
$

 
$
647

Agency - Residential
 
576

 
14

 

 
590

Total held-to-maturity securities (1)
 
$
1,211

 
$
26

 
$

 
$
1,237

December 31, 2015
 
 
 
 
 
 
 
 
Available-for-sale securities
 
 
 
 
 
 
 
 
Agency - Commercial
 
$
766

 
$
3

 
$
(3
)
 
$
766

Agency - Residential
 
514

 
2

 
(2
)
 
514

Municipal obligations
 
14

 

 

 
14

Total available-for-sale securities (1)
 
$
1,294

 
$
5

 
$
(5
)
 
$
1,294

Held-to-maturity securities
 
 
 
 
 
 
 
 
Agency - Commercial
 
$
634

 
$

 
$
(2
)
 
$
632

Agency - Residential
 
634

 

 
(4
)
 
630

Total held-to-maturity securities (1)
 
$
1,268

 
$

 
$
(6
)
 
$
1,262


(1)
There were no securities of a single issuer, which are not governmental or government-sponsored, that exceeded 10 percent of stockholders’ equity at June 30, 2016 or December 31, 2015.