Quarterly report pursuant to Section 13 or 15(d)

Fair Value Measurements - Schedule of Reconciliation of Level 3 Investments Securities (Parenthetical) (Detail)

v3.8.0.1
Fair Value Measurements - Schedule of Reconciliation of Level 3 Investments Securities (Parenthetical) (Detail)
$ in Millions
Sep. 30, 2017
USD ($)
Security
Dec. 31, 2016
USD ($)
Security
Fair Value Disclosures [Abstract]    
Investment grade rated debt held for more than 12 months $ 10 $ 10
Securities in unrealized loss position $ 1 $ 1
Securities in unrealized loss position | Security 0 0