v3.8.0.1
Fair Value Disclosures - Changes in Level 3 Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value, beginning balance $ 116 $ 143
Realized and Unrealized Gains (Losses) in Earnings and OCI, Assets   1
Purchases, Assets 31  
Transfers out of Level 3, Assets   (31)
Assets measured at fair value, ending balance 147 113
Available-for-sale Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value, beginning balance   24
Purchases, Assets 26  
Transfers out of Level 3, Assets   (24)
Assets measured at fair value, ending balance 26  
Consolidated Variable Interest Entities [Member] | Other Liabilities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Liabilities measured at fair value, beginning balance 236 115
Realized and Unrealized Gains (Losses) in Earnings and OCI, Liabilities (6) 2
Liabilities measured at fair value, ending balance 242 113
Total Net Unrealized Gains (Losses) Included in Earnings (6) 2
Consolidated Variable Interest Entities [Member] | Private/ Public Equity [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value, beginning balance 116 112
Realized and Unrealized Gains (Losses) in Earnings and OCI, Assets   1
Assets measured at fair value, ending balance 116 113
Total Net Unrealized Gains (Losses) Included in Earnings   1
Trading Securities [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value, beginning balance   7
Purchases, Assets 5  
Transfers out of Level 3, Assets   (7)
Assets measured at fair value, ending balance 5  
Investments [Member]    
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]    
Assets measured at fair value, beginning balance   31
Purchases, Assets 31  
Transfers out of Level 3, Assets   $ (31)
Assets measured at fair value, ending balance $ 31