DEBT - Credit Agreement (Detail)	12 Months Ended
	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Debt Instrument [Line Items]
Actual net worth	$ 9,842,000,000	$ 10,685,000,000	$ 10,346,000,000	$ 9,646,000,000
Borrowings outstanding under credit agreement	0
Outstanding letters of credit	0
Remaining borrowing capacity	$ 2,000,000,000
Revolving Credit Facility | Line of Credit | Unsecured Revolving Credit Agreement, Expires July 2018
Debt Instrument [Line Items]
Term	5 years
Maximum borrowing capacity	$ 1,000,000,000.0
Revolving Credit Facility | Line of Credit | Unsecured Revolving Credit Agreement Expires May 2022
Debt Instrument [Line Items]
Term	5 years
Maximum borrowing capacity	$ 2,000,000,000
Revolving Credit Facility | Line of Credit | Credit Agreement
Debt Instrument [Line Items]
Maximum borrowing capacity	2,500,000,000
Minimum level of net worth required	$ 9,200,000,000.0
Maximum leverage ratios for new credit agreement	3.0
Actual net worth	$ 9,800,000,000
Actual leverage ratio	1.0
Uncommitted incremental loan facility	$ 500,000,000
Revolving Credit Facility | Line of Credit | LIBOR | Credit Agreement
Debt Instrument [Line Items]
Basis points spread over LIBOR	1.10%
Facility fee that is dependent upon credit rating, basis points	0.15%
Revolving Credit Facility | Line of Credit | LIBOR | Credit Agreement | Minimum
Debt Instrument [Line Items]
Basis points spread over LIBOR	0.91%
Facility fee that is dependent upon credit rating, basis points	0.09%
Revolving Credit Facility | Line of Credit | LIBOR | Credit Agreement | Maximum
Debt Instrument [Line Items]
Basis points spread over LIBOR	1.50%
Facility fee that is dependent upon credit rating, basis points	0.25%