Fair Value Measurements (Assets Measured At Fair Value Using Significant Unobservable Inputs) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	$ 39	$ 37	$ 41	$ 16
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets	0	0	0	0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)	0	3	1	2
Net Realized Gains/ (Losses), Assets	1	0	1	1
Purchases, Assets	17	0	23	23	[1],[2]
Sales, Assets	(5)	(3)	(14)	(5)
Settlements, Assets	0	0	0	0
Balance-End of Period, Assets	52	37	52	37
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0	0	0
Short-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	7	50	25	0
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets	0	0	0	0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0	0	0
Net Realized Gains/ (Losses), Assets	0	0	0	0
Purchases, Assets	1	12	15	62	[1],[2]
Sales, Assets	0	0	0	0
Settlements, Assets	(8)	0	(40)	0
Balance-End of Period, Assets	0	62	0	62
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)		0	0	0
Other Long-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	243	216	225	212
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets	0	0	0	0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)	0	4	3	4
Net Realized Gains/ (Losses), Assets	0	0	0	0
Purchases, Assets	15	8	39	22	[1],[2]
Sales, Assets	0	0	0	0
Settlements, Assets	(6)	(5)	(15)	(15)
Balance-End of Period, Assets	252	223	252	223
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0	0	0
Available-for-sale Securities [Member] | Foreign Government Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	85	87	74	57
Transfers Into Level 3, Asset	0	0	0	9
Transfers out of Level 3, Assets	(3)	0	(3)	(2)
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)	1	(1)	3	8
Net Realized Gains/ (Losses), Assets	0	0	1	(6)
Purchases, Assets	24	20	57	52	[1],[2]
Sales, Assets	(14)	(2)	(36)	(10)
Settlements, Assets	(3)	(1)	(6)	(5)
Balance-End of Period, Assets	90	103	90	103
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0	0	(5)
Available-for-sale Securities [Member] | Corporate [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	747	281	681	174
Transfers Into Level 3, Asset	111	0	168	18
Transfers out of Level 3, Assets	(26)	0	(93)	0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)	(1)	6	(9)	17
Net Realized Gains/ (Losses), Assets	0	(4)	(1)	(12)
Purchases, Assets	169	348	390	472	[1],[2]
Sales, Assets	(24)	(18)	(79)	(48)
Settlements, Assets	(57)	(7)	(138)	(15)
Balance-End of Period, Assets	919	606	919	606
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	(4)	0	(11)
Available-for-sale Securities [Member] | Collateralized Mortgage Backed Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	45	49	45	53
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets	0	0	0	0
Asset, Net realized Gain (Loss) Included in Other Comprehensive Income (Loss)	0	0	0	0
Net Realized Gains/ (Losses), Assets	0	0	0	0
Purchases, Assets	7	0	8	1	[1],[2]
Sales, Assets	0	(3)	(1)	(8)
Settlements, Assets	(8)	0	(8)	0
Balance-End of Period, Assets	44	46	44	46
Fair Value, Assets Measured on Recurring Basis, Change in Unrealized Gain (Loss)	$ 0	$ 0	$ 0	$ 0

[1] Includes acquired invested assets as a result of the Chubb Corp acquisition.

[2] Our GLB reinsurance product meets the definition of a derivative instrument for accounting purposes and is accordingly carried at fair value. Excluded from the table above is the portion of the GLB derivative liability classified as Future policy benefits in the Consolidated balance sheets. The liability for GLB reinsurance was $1.2 billion at September 30, 2016, and $888 million at December 31, 2015, which includes a fair value derivative adjustment of $883 million and $609 million, respectively.