Derivative Instruments - Additional Information (Details) € in Millions, $ in Millions, $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2018 EUR (€)	Dec. 31, 2017 CAD ($)	Dec. 31, 2017 USD ($)
Maximum
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional value	$ 124
Interest expense, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Amount of pre-tax losses in AOCI expect to be reclassified into interest expense	12
Interest rate swaps
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional value	3,500		$ 2,500
Interest rate swaps | Interest expense, net
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Net unrealized loss remaining in AOCI			$ 85
Cross currency interest rate contract
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Cash received on hedge		$ 764
Net unrealized gain remaining in AOCI		$ 533
Cross currency interest rate contract | Fixed income interest rate
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional value	400				$ 6,754	$ 5,000
Hedge funds | Cross currency interest rate contract | Fixed income interest rate
Derivative Instruments and Hedging Activities Disclosures [Line Items]
Notional value	$ 1,200			€ 1,108