Debt (FHLB Advances) (Details) - USD ($)
$ in Millions |
Jun. 30, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
Dec. 31, 2013 |
| Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items] |
|
|
|
|
| Short-term debt |
$ 1,069
|
$ 2,116
|
|
|
| Federal Home Loan Bank advances (includes both long-term and short-term) |
$ 2,646
|
$ 3,541
|
$ 514
|
$ 988
|
| Federal Home Loan Bank Advances, Rate (as a percent) |
0.77%
|
0.59%
|
|
|
| Current portion of fixed rate advances |
$ 1,577
|
$ 1,425
|
|
|
| Short-term adjustable rate |
|
|
|
|
| Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items] |
|
|
|
|
| Short-term debt |
1
|
0
|
|
|
| Federal Home Loan Bank advances (includes both long-term and short-term) |
|
0
|
0
|
216
|
| Short-term fixed rate term advances |
|
|
|
|
| Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items] |
|
|
|
|
| Federal Home Loan Bank advances (includes both long-term and short-term) |
$ 1,068
|
$ 2,116
|
214
|
772
|
| Federal Home Loan Bank Advances, Rate (as a percent) |
0.40%
|
0.32%
|
|
|
| Long-term LIBOR adjustable advances |
|
|
|
|
| Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items] |
|
|
|
|
| Federal Home Loan Bank advances (includes both long-term and short-term) |
$ 1,025
|
$ 825
|
0
|
0
|
| Federal Home Loan Bank Advances, Rate (as a percent) |
0.80%
|
0.70%
|
|
|
| Long-term fixed rate advances |
|
|
|
|
| Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items] |
|
|
|
|
| Federal Home Loan Bank advances (includes both long-term and short-term) |
$ 552
|
$ 600
|
$ 300
|
$ 0
|
| Federal Home Loan Bank Advances, Rate (as a percent) |
1.44%
|
1.37%
|
|
|
| Long-term fixed rate advances |
|
|
|
|
| Federal Home Loan Bank, Advances, Branch of FHLB Bank [Line Items] |
|
|
|
|
| Current portion of fixed rate advances |
$ 125
|
$ 175
|
|
|