Gross Unrealized Losses and Fair Value of Corporate Securities Based on Industries (Detail) $ in Millions	Sep. 30, 2024 USD ($) Securities	Dec. 31, 2023 USD ($) Securities
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 620	$ 1,459
Less than 12 months, Gross unrealized losses	$ (32)	$ (40)
Less than 12 months, Number of securities in a continuous loss position | Securities	100	223
12 months or more, Fair value	$ 26,356	$ 29,031
12 months or more, Gross unrealized losses	$ (2,822)	$ (3,523)
12 months or more, Number of securities in a continuous loss position | Securities	3,412	3,940
Fair value	$ 26,976	$ 30,490
Gross unrealized losses	$ (2,854)	$ (3,563)
Number of securities in a continuous loss position | Securities	3,512	4,163
U.S. corporate
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 369	$ 1,054
Less than 12 months, Gross unrealized losses	$ (26)	$ (30)
Less than 12 months, Number of securities in a continuous loss position | Securities	59	142
12 months or more, Fair value	$ 15,802	$ 17,019
12 months or more, Gross unrealized losses	$ (1,612)	$ (1,994)
12 months or more, Number of securities in a continuous loss position | Securities	1,936	2,164
Fair value	$ 16,171	$ 18,073
Gross unrealized losses	$ (1,638)	$ (2,024)
Number of securities in a continuous loss position | Securities	1,995	2,306
U.S. corporate | Utilities
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 177
Less than 12 months, Gross unrealized losses	$ 0	$ (2)
Less than 12 months, Number of securities in a continuous loss position | Securities	0	21
12 months or more, Fair value	$ 2,104	$ 2,129
12 months or more, Gross unrealized losses	$ (305)	$ (350)
12 months or more, Number of securities in a continuous loss position | Securities	299	308
Fair value	$ 2,104	$ 2,306
Gross unrealized losses	$ (305)	$ (352)
Number of securities in a continuous loss position | Securities	299	329
U.S. corporate | Energy
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 100	$ 122
Less than 12 months, Gross unrealized losses	$ (13)	$ (2)
Less than 12 months, Number of securities in a continuous loss position | Securities	15	20
12 months or more, Fair value	$ 1,151	$ 1,343
12 months or more, Gross unrealized losses	$ (100)	$ (141)
12 months or more, Number of securities in a continuous loss position | Securities	141	168
Fair value	$ 1,251	$ 1,465
Gross unrealized losses	$ (113)	$ (143)
Number of securities in a continuous loss position | Securities	156	188
U.S. corporate | Finance and insurance
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 274
Less than 12 months, Gross unrealized losses	$ 0	$ (8)
Less than 12 months, Number of securities in a continuous loss position | Securities	0	42
12 months or more, Fair value	$ 4,838	$ 5,192
12 months or more, Gross unrealized losses	$ (476)	$ (626)
12 months or more, Number of securities in a continuous loss position | Securities	573	645
Fair value	$ 4,838	$ 5,466
Gross unrealized losses	$ (476)	$ (634)
Number of securities in a continuous loss position | Securities	573	687
U.S. corporate | Consumer-non-cyclical
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 87	$ 173
Less than 12 months, Gross unrealized losses	$ (1)	$ (6)
Less than 12 months, Number of securities in a continuous loss position | Securities	14	18
12 months or more, Fair value	$ 2,458	$ 2,529
12 months or more, Gross unrealized losses	$ (225)	$ (266)
12 months or more, Number of securities in a continuous loss position | Securities	258	280
Fair value	$ 2,545	$ 2,702
Gross unrealized losses	$ (226)	$ (272)
Number of securities in a continuous loss position | Securities	272	298
U.S. corporate | Technology and communications
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 43	$ 105
Less than 12 months, Gross unrealized losses	$ (3)	$ (6)
Less than 12 months, Number of securities in a continuous loss position | Securities	7	19
12 months or more, Fair value	$ 1,889	$ 2,100
12 months or more, Gross unrealized losses	$ (206)	$ (233)
12 months or more, Number of securities in a continuous loss position | Securities	233	269
Fair value	$ 1,932	$ 2,205
Gross unrealized losses	$ (209)	$ (239)
Number of securities in a continuous loss position | Securities	240	288
U.S. corporate | Industrial
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 30	$ 50
Less than 12 months, Gross unrealized losses	$ (1)	$ (1)
Less than 12 months, Number of securities in a continuous loss position | Securities	7	6
12 months or more, Fair value	$ 603	$ 702
12 months or more, Gross unrealized losses	$ (66)	$ (87)
12 months or more, Number of securities in a continuous loss position | Securities	82	96
Fair value	$ 633	$ 752
Gross unrealized losses	$ (67)	$ (88)
Number of securities in a continuous loss position | Securities	89	102
U.S. corporate | Capital goods
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 66	$ 0
Less than 12 months, Gross unrealized losses	$ (6)	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	9	0
12 months or more, Fair value	$ 1,082	$ 1,193
12 months or more, Gross unrealized losses	$ (91)	$ (118)
12 months or more, Number of securities in a continuous loss position | Securities	135	150
Fair value	$ 1,148	$ 1,193
Gross unrealized losses	$ (97)	$ (118)
Number of securities in a continuous loss position | Securities	144	150
U.S. corporate | Consumer-cyclical
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 43	$ 88
Less than 12 months, Gross unrealized losses	$ (2)	$ (1)
Less than 12 months, Number of securities in a continuous loss position | Securities	7	11
12 months or more, Fair value	$ 950	$ 1,073
12 months or more, Gross unrealized losses	$ (76)	$ (95)
12 months or more, Number of securities in a continuous loss position | Securities	124	148
Fair value	$ 993	$ 1,161
Gross unrealized losses	$ (78)	$ (96)
Number of securities in a continuous loss position | Securities	131	159
U.S. corporate | Transportation
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 65
Less than 12 months, Gross unrealized losses	$ 0	$ (4)
Less than 12 months, Number of securities in a continuous loss position | Securities	0	5
12 months or more, Fair value	$ 587	$ 621
12 months or more, Gross unrealized losses	$ (56)	$ (65)
12 months or more, Number of securities in a continuous loss position | Securities	74	82
Fair value	$ 587	$ 686
Gross unrealized losses	$ (56)	$ (69)
Number of securities in a continuous loss position | Securities	74	87
U.S. corporate | Other
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 0
Less than 12 months, Gross unrealized losses	$ 0	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	0	0
12 months or more, Fair value	$ 140	$ 137
12 months or more, Gross unrealized losses	$ (11)	$ (13)
12 months or more, Number of securities in a continuous loss position | Securities	17	18
Fair value	$ 140	$ 137
Gross unrealized losses	$ (11)	$ (13)
Number of securities in a continuous loss position | Securities	17	18
Non-U.S. corporate
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 15	$ 157
Less than 12 months, Gross unrealized losses	$ (2)	$ (5)
Less than 12 months, Number of securities in a continuous loss position | Securities	2	19
12 months or more, Fair value	$ 4,428	$ 5,180
12 months or more, Gross unrealized losses	$ (402)	$ (528)
12 months or more, Number of securities in a continuous loss position | Securities	556	684
Fair value	$ 4,443	$ 5,337
Gross unrealized losses	$ (404)	$ (533)
Number of securities in a continuous loss position | Securities	558	703
Non-U.S. corporate | Utilities
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 0
Less than 12 months, Gross unrealized losses	$ 0	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	0	0
12 months or more, Fair value	$ 523	$ 609
12 months or more, Gross unrealized losses	$ (52)	$ (55)
12 months or more, Number of securities in a continuous loss position | Securities	56	68
Fair value	$ 523	$ 609
Gross unrealized losses	$ (52)	$ (55)
Number of securities in a continuous loss position | Securities	56	68
Non-U.S. corporate | Energy
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 39
Less than 12 months, Gross unrealized losses	$ 0	$ (1)
Less than 12 months, Number of securities in a continuous loss position | Securities	0	4
12 months or more, Fair value	$ 452	$ 487
12 months or more, Gross unrealized losses	$ (35)	$ (44)
12 months or more, Number of securities in a continuous loss position | Securities	49	59
Fair value	$ 452	$ 526
Gross unrealized losses	$ (35)	$ (45)
Number of securities in a continuous loss position | Securities	49	63
Non-U.S. corporate | Finance and insurance
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 100
Less than 12 months, Gross unrealized losses	$ 0	$ (2)
Less than 12 months, Number of securities in a continuous loss position | Securities	0	10
12 months or more, Fair value	$ 1,178	$ 1,358
12 months or more, Gross unrealized losses	$ (91)	$ (138)
12 months or more, Number of securities in a continuous loss position | Securities	159	203
Fair value	$ 1,178	$ 1,458
Gross unrealized losses	$ (91)	$ (140)
Number of securities in a continuous loss position | Securities	159	213
Non-U.S. corporate | Consumer-non-cyclical
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 15	$ 0
Less than 12 months, Gross unrealized losses	$ (2)	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	2	0
12 months or more, Fair value	$ 387	$ 471
12 months or more, Gross unrealized losses	$ (51)	$ (61)
12 months or more, Number of securities in a continuous loss position | Securities	45	55
Fair value	$ 402	$ 471
Gross unrealized losses	$ (53)	$ (61)
Number of securities in a continuous loss position | Securities	47	55
Non-U.S. corporate | Technology and communications
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 0
Less than 12 months, Gross unrealized losses	$ 0	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	0	0
12 months or more, Fair value	$ 517	$ 659
12 months or more, Gross unrealized losses	$ (49)	$ (65)
12 months or more, Number of securities in a continuous loss position | Securities	61	83
Fair value	$ 517	$ 659
Gross unrealized losses	$ (49)	$ (65)
Number of securities in a continuous loss position | Securities	61	83
Non-U.S. corporate | Industrial
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 18
Less than 12 months, Gross unrealized losses	$ 0	$ (2)
Less than 12 months, Number of securities in a continuous loss position | Securities	0	5
12 months or more, Fair value	$ 386	$ 436
12 months or more, Gross unrealized losses	$ (35)	$ (47)
12 months or more, Number of securities in a continuous loss position | Securities	53	61
Fair value	$ 386	$ 454
Gross unrealized losses	$ (35)	$ (49)
Number of securities in a continuous loss position | Securities	53	66
Non-U.S. corporate | Capital goods
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 0
Less than 12 months, Gross unrealized losses	$ 0	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	0	0
12 months or more, Fair value	$ 341	$ 384
12 months or more, Gross unrealized losses	$ (31)	$ (38)
12 months or more, Number of securities in a continuous loss position | Securities	44	49
Fair value	$ 341	$ 384
Gross unrealized losses	$ (31)	$ (38)
Number of securities in a continuous loss position | Securities	44	49
Non-U.S. corporate | Consumer-cyclical
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 0
Less than 12 months, Gross unrealized losses	$ 0	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	0	0
12 months or more, Fair value	$ 122	$ 188
12 months or more, Gross unrealized losses	$ (10)	$ (17)
12 months or more, Number of securities in a continuous loss position | Securities	20	26
Fair value	$ 122	$ 188
Gross unrealized losses	$ (10)	$ (17)
Number of securities in a continuous loss position | Securities	20	26
Non-U.S. corporate | Transportation
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 0
Less than 12 months, Gross unrealized losses	$ 0	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	0	0
12 months or more, Fair value	$ 256	$ 216
12 months or more, Gross unrealized losses	$ (18)	$ (20)
12 months or more, Number of securities in a continuous loss position | Securities	34	30
Fair value	$ 256	$ 216
Gross unrealized losses	$ (18)	$ (20)
Number of securities in a continuous loss position | Securities	34	30
Non-U.S. corporate | Other
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 0	$ 0
Less than 12 months, Gross unrealized losses	$ 0	$ 0
Less than 12 months, Number of securities in a continuous loss position | Securities	0	0
12 months or more, Fair value	$ 266	$ 372
12 months or more, Gross unrealized losses	$ (30)	$ (43)
12 months or more, Number of securities in a continuous loss position | Securities	35	50
Fair value	$ 266	$ 372
Gross unrealized losses	$ (30)	$ (43)
Number of securities in a continuous loss position | Securities	35	50
Corporate Debt Securities
Available for Sale Securities Continuous Unrealized Loss Position [Line Items]
Less than 12 months, Fair value	$ 384	$ 1,211
Less than 12 months, Gross unrealized losses	$ (28)	$ (35)
Less than 12 months, Number of securities in a continuous loss position | Securities	61	161
12 months or more, Fair value	$ 20,230	$ 22,199
12 months or more, Gross unrealized losses	$ (2,014)	$ (2,522)
12 months or more, Number of securities in a continuous loss position | Securities	2,492	2,848
Fair value	$ 20,614	$ 23,410
Gross unrealized losses	$ (2,042)	$ (2,557)
Number of securities in a continuous loss position | Securities	2,553	3,009