FAIR VALUE MEASUREMENTS - Fair Value Hierarchy Levels of Assets and Liabilities Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Assets:
Available-for-sale securities	$ 85,336	$ 76,702
Asset derivatives	331	1,207
Other investments	57	276
Cash and cash equivalents	3,491	4,859
Total assets	89,215	83,044
Liabilities:
Liability derivatives	474	1,998
Total liabilities	474	1,998
Foreign currency swaps
Assets:
Asset derivatives	296	490
Liabilities:
Liability derivatives	197	230
Foreign currency forwards
Assets:
Asset derivatives	22	672
Liabilities:
Liability derivatives	274	1,717
Foreign currency options
Assets:
Asset derivatives	12	43
Liabilities:
Liability derivatives	3	51
Credit default swaps
Assets:
Asset derivatives	1	2
Fixed maturities
Assets:
Available-for-sale securities	82,524	73,760
Fixed maturities | Government and agencies
Assets:
Available-for-sale securities	31,230	26,214
Fixed maturities | Municipalities
Assets:
Available-for-sale securities	1,370	1,295
Fixed maturities | Mortgage- and asset-backed securities
Assets:
Available-for-sale securities	444	1,337
Fixed maturities | Public utilities
Assets:
Available-for-sale securities	7,954	7,683
Fixed maturities | Sovereign and supranational
Assets:
Available-for-sale securities	1,909	1,469
Fixed maturities | Banks/financial institutions
Assets:
Available-for-sale securities	7,377	6,063
Fixed maturities | Other corporate
Assets:
Available-for-sale securities	32,240	29,699
Perpetual securities
Assets:
Available-for-sale securities	1,789	1,633
Perpetual securities | Banks/financial institutions
Assets:
Available-for-sale securities	1,556	1,420
Perpetual securities | Other corporate
Assets:
Available-for-sale securities	233	213
Equity securities
Assets:
Available-for-sale securities	1,023	1,309
Level 1
Assets:
Available-for-sale securities	31,110	26,687
Asset derivatives	0	0
Other investments	57	276
Cash and cash equivalents	3,491	4,859
Total assets	34,658	31,822
Liabilities:
Total liabilities	0	0
Level 1 | Foreign currency swaps
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 1 | Foreign currency forwards
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 1 | Foreign currency options
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 1 | Credit default swaps
Assets:
Asset derivatives	0	0
Level 1 | Fixed maturities
Assets:
Available-for-sale securities	30,109	25,387
Level 1 | Fixed maturities | Government and agencies
Assets:
Available-for-sale securities	30,109	25,387
Level 1 | Fixed maturities | Municipalities
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Mortgage- and asset-backed securities
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Public utilities
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Sovereign and supranational
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Banks/financial institutions
Assets:
Available-for-sale securities	0	0
Level 1 | Fixed maturities | Other corporate
Assets:
Available-for-sale securities	0	0
Level 1 | Perpetual securities
Assets:
Available-for-sale securities	0	0
Level 1 | Perpetual securities | Banks/financial institutions
Assets:
Available-for-sale securities	0	0
Level 1 | Perpetual securities | Other corporate
Assets:
Available-for-sale securities	0	0
Level 1 | Equity securities
Assets:
Available-for-sale securities	1,001	1,300
Level 2
Assets:
Available-for-sale securities	53,796	49,773
Asset derivatives	180	1,080
Other investments	0	0
Cash and cash equivalents	0	0
Total assets	53,976	50,853
Liabilities:
Total liabilities	346	1,852
Level 2 | Foreign currency swaps
Assets:
Asset derivatives	146	365
Liabilities:
Liability derivatives	69	84
Level 2 | Foreign currency forwards
Assets:
Asset derivatives	22	672
Liabilities:
Liability derivatives	274	1,717
Level 2 | Foreign currency options
Assets:
Asset derivatives	12	43
Liabilities:
Liability derivatives	3	51
Level 2 | Credit default swaps
Assets:
Asset derivatives	0	0
Level 2 | Fixed maturities
Assets:
Available-for-sale securities	52,001	48,134
Level 2 | Fixed maturities | Government and agencies
Assets:
Available-for-sale securities	1,121	827
Level 2 | Fixed maturities | Municipalities
Assets:
Available-for-sale securities	1,370	1,295
Level 2 | Fixed maturities | Mortgage- and asset-backed securities
Assets:
Available-for-sale securities	269	1,139
Level 2 | Fixed maturities | Public utilities
Assets:
Available-for-sale securities	7,886	7,667
Level 2 | Fixed maturities | Sovereign and supranational
Assets:
Available-for-sale securities	1,909	1,469
Level 2 | Fixed maturities | Banks/financial institutions
Assets:
Available-for-sale securities	7,352	6,038
Level 2 | Fixed maturities | Other corporate
Assets:
Available-for-sale securities	32,094	29,699
Level 2 | Perpetual securities
Assets:
Available-for-sale securities	1,789	1,633
Level 2 | Perpetual securities | Banks/financial institutions
Assets:
Available-for-sale securities	1,556	1,420
Level 2 | Perpetual securities | Other corporate
Assets:
Available-for-sale securities	233	213
Level 2 | Equity securities
Assets:
Available-for-sale securities	6	6
Level 3
Assets:
Available-for-sale securities	430	242
Asset derivatives	151	127
Other investments	0	0
Cash and cash equivalents	0	0
Total assets	581	369
Liabilities:
Total liabilities	128	146
Level 3 | Foreign currency swaps
Assets:
Asset derivatives	150	125
Liabilities:
Liability derivatives	128	146
Level 3 | Foreign currency forwards
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 3 | Foreign currency options
Assets:
Asset derivatives	0	0
Liabilities:
Liability derivatives	0	0
Level 3 | Credit default swaps
Assets:
Asset derivatives	1	2
Level 3 | Fixed maturities
Assets:
Available-for-sale securities	414	239
Level 3 | Fixed maturities | Government and agencies
Assets:
Available-for-sale securities	0	0
Level 3 | Fixed maturities | Municipalities
Assets:
Available-for-sale securities	0	0
Level 3 | Fixed maturities | Mortgage- and asset-backed securities
Assets:
Available-for-sale securities	175	198
Level 3 | Fixed maturities | Public utilities
Assets:
Available-for-sale securities	68	16
Level 3 | Fixed maturities | Sovereign and supranational
Assets:
Available-for-sale securities	0	0
Level 3 | Fixed maturities | Banks/financial institutions
Assets:
Available-for-sale securities	25	25
Level 3 | Fixed maturities | Other corporate
Assets:
Available-for-sale securities	146	0
Level 3 | Perpetual securities
Assets:
Available-for-sale securities	0	0
Level 3 | Perpetual securities | Banks/financial institutions
Assets:
Available-for-sale securities	0	0
Level 3 | Perpetual securities | Other corporate
Assets:
Available-for-sale securities	0	0
Level 3 | Equity securities
Assets:
Available-for-sale securities	$ 16	$ 3