Assets Held for Sale - Additional Information (Detail) - USD ($) $ in Millions |
12 Months Ended | |||
|---|---|---|---|---|
Feb. 06, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Dec. 31, 2014 |
|
| Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] | ||||
| Cash proceeds | $ 20 | $ 1,605 | $ 1 | |
| SP [Member] | Disposal Group, Held-for-sale, Not Discontinued Operations [Member] | Subsequent Event [Member] | ||||
| Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] | ||||
| Cash proceeds | $ 2,750 | |||