Changes in Fair Value of Level 3 Plan Assets (Detail) - USD ($) $ in Millions |
12 Months Ended | |
|---|---|---|
Dec. 31, 2016 |
Dec. 31, 2015 |
|
| Defined Benefit Plan Disclosure [Line Items] | ||
| Beginning Balance | $ 231 | $ 61 |
| Realized losses, net | (6) | (12) |
| Unrealized gains, net | 3 | 7 |
| Purchases, sales and settlements, net | (207) | (22) |
| Transfers into (out of) Level 3, net | 5 | 197 |
| Ending Balance | 26 | 231 |
| Private equity funds | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Beginning Balance | 200 | |
| Purchases, sales and settlements, net | (200) | |
| Transfers into (out of) Level 3, net | 200 | |
| Ending Balance | 200 | |
| Other | ||
| Defined Benefit Plan Disclosure [Line Items] | ||
| Beginning Balance | 31 | 61 |
| Realized losses, net | (6) | (12) |
| Unrealized gains, net | 3 | 7 |
| Purchases, sales and settlements, net | (7) | (22) |
| Transfers into (out of) Level 3, net | 5 | (3) |
| Ending Balance | $ 26 | $ 31 |