Investments - Amortized Cost and Fair Values of Securities (Detail) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	$ 37,669	$ 38,202
Gross Unrealized Gains	3,891	3,640
Gross Unrealized Losses	208	229
Estimated Fair Value	41,352	41,613
Unrealized OTTI Losses (Gains)	(54)	(55)
Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	36,997	37,469
Gross Unrealized Gains	3,801	3,530
Gross Unrealized Losses	90	114
Estimated Fair Value	40,708	40,885
Unrealized OTTI Losses (Gains)	(54)	(55)
Corporate and Other Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	16,737	17,226
Gross Unrealized Gains	1,867	1,721
Gross Unrealized Losses	45	61
Estimated Fair Value	18,559	18,886
States, Municipalities and Political Subdivisions [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	11,407	11,285
Gross Unrealized Gains	1,536	1,463
Gross Unrealized Losses	9	8
Estimated Fair Value	12,934	12,740
Residential Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	4,998	5,028
Gross Unrealized Gains	241	218
Gross Unrealized Losses	13	13
Estimated Fair Value	5,226	5,233
Unrealized OTTI Losses (Gains)	(51)	(53)
Commercial Mortgage-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	2,151	2,056
Gross Unrealized Gains	114	93
Gross Unrealized Losses	5	5
Estimated Fair Value	2,260	2,144
Unrealized OTTI Losses (Gains)	(3)	(2)
Other Asset-Backed [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	1,109	1,234
Gross Unrealized Gains	15	11
Gross Unrealized Losses	1	10
Estimated Fair Value	1,123	1,235
Total Asset-Backed [Member] | Fixed Maturity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	8,258	8,318
Gross Unrealized Gains	370	322
Gross Unrealized Losses	19	28
Estimated Fair Value	8,609	8,612
Unrealized OTTI Losses (Gains)	(54)	(55)
U.S. Treasury and Obligations of Government-Sponsored Enterprises [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	24	26
Gross Unrealized Gains	6	5
Estimated Fair Value	30	31
Foreign Government [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	390	438
Gross Unrealized Gains	19	16
Estimated Fair Value	409	454
Redeemable Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	39	39
Gross Unrealized Gains	3	3
Estimated Fair Value	42	42
Total Fixed Maturities Available-for-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	36,855	37,332
Gross Unrealized Gains	3,801	3,530
Gross Unrealized Losses	73	97
Estimated Fair Value	40,583	40,765
Unrealized OTTI Losses (Gains)	(54)	(55)
Fixed Maturities Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	142	137
Gross Unrealized Losses	17	17
Estimated Fair Value	125	120
Common Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	41	38
Gross Unrealized Gains	9	9
Estimated Fair Value	50	47
Preferred Stock [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	172	172
Gross Unrealized Gains	7	5
Gross Unrealized Losses	4	2
Estimated Fair Value	175	175
Total Equity Securities Available-for-Sale [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	213	210
Gross Unrealized Gains	16	14
Gross Unrealized Losses	4	2
Estimated Fair Value	225	222
Equity Securities Trading [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	459	523
Gross Unrealized Gains	74	96
Gross Unrealized Losses	114	113
Estimated Fair Value	419	506
Equity Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Cost or Amortized Cost	672	733
Gross Unrealized Gains	90	110
Gross Unrealized Losses	118	115
Estimated Fair Value	$ 644	$ 728