Derivative Instruments - Schedule of Series of Forward Starting Swaps Each with a Term of One Year (Detail) $ in Millions	Dec. 31, 2015 USD ($)
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional balance of outstanding contracts	$ 3,339
Year 2016
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional balance of outstanding contracts	1,010
Year 2017
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional balance of outstanding contracts	697
Year 2018
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional balance of outstanding contracts	544
Year 2019
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional balance of outstanding contracts	544
Year 2020
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional balance of outstanding contracts	272
Year 2021
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional balance of outstanding contracts	$ 272