Fair Value Disclosures - Fair Value of Financial Assets and Financial Liabilities (Parenthetical) (Detail) - USD ($) $ / shares in Units, $ in Millions |
Jun. 30, 2017 |
Dec. 31, 2016 |
Jun. 30, 2016 |
Dec. 31, 2015 |
|---|---|---|---|---|
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||
| Cash and cash equivalents | $ 5,508 | $ 6,091 | $ 5,065 | $ 6,083 |
| Money market valuation per share floor | $ 1.00 | |||
| Money Market Funds [Member] | ||||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||
| Cash and cash equivalents | $ 136 | 132 | ||
| Consolidated Variable Interest Entities [Member] | ||||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||
| Cash and cash equivalents | 74 | 84 | ||
| Consolidated Variable Interest Entities [Member] | Money Market Funds [Member] | ||||
| Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] | ||||
| Cash and cash equivalents | $ 21 | $ 13 |