Fair Value Measurements (Assets Measured At Fair Value Using Significant Unobservable Inputs) (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Document Period End Date			Sep. 30, 2016
Foreign [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	$ 87	$ 56	$ 57	$ 22
Transfers Into Level 3, Asset	0	1	9	29
Transfers out of Level 3, Assets			(2)
Change in Net Unrealized Gains (Losses) included in OCI, Assets	1	(1)	8	(1)
Net Realized Gains/Losses, Assets	0	(1)	(6)	(1)
Purchases, Assets	20	0	52	9
Sales, Assets	(2)	0	(10)	(1)
Settlements, Assets	(1)	(4)	(5)	(4)
Balance-End of Period, Assets	103	53	103	53
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	(1)	(5)	(1)
Corporate [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	281	167	174	187
Transfers Into Level 3, Asset	0	2	18	15
Transfers out of Level 3, Assets			0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(6)	(1)	17	1
Net Realized Gains/Losses, Assets	(4)	(1)	(12)	(4)
Purchases, Assets	348	22	472	38
Sales, Assets	(18)	(5)	(48)	(10)
Settlements, Assets	(7)	(3)	(15)	(44)
Balance-End of Period, Assets	606	183	606	183
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	(4)	0	(11)	(2)
Collateralized Mortgage Backed Securities [Member] | Available-for-sale Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	49	55	53	15
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets			0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0	0	0	0
Net Realized Gains/Losses, Assets	0	0	0	0
Purchases, Assets	0	0	1	41
Sales, Assets	(3)	(1)	(8)	(1)
Settlements, Assets	0	0	0	(1)
Balance-End of Period, Assets	46	54	46	54
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	0	0	0
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	37	2	16	2
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets			0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(3)	(2)	2	2
Net Realized Gains/Losses, Assets	0	(1)	1	(2)
Purchases, Assets	0	1	23	2
Sales, Assets	(3)	0	(5)	0
Settlements, Assets	0	0	0	0
Balance-End of Period, Assets	37	4	37	4
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0	(1)	0	(2)
Short-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	50		0
Transfers Into Level 3, Asset	0		0
Transfers out of Level 3, Assets			0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	0		0
Net Realized Gains/Losses, Assets	0		0
Purchases, Assets	12		62
Sales, Assets	0		0
Settlements, Assets	0		0
Balance-End of Period, Assets	62		62
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	0		0
Other Long-term Investments [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance- Beginning of Period, Assets	216	214	212	204
Transfers Into Level 3, Asset	0	0	0	0
Transfers out of Level 3, Assets			0
Change in Net Unrealized Gains (Losses) included in OCI, Assets	(4)	7	4	(7)
Net Realized Gains/Losses, Assets	0	0	0	0
Purchases, Assets	8	5	22	21
Sales, Assets	0	0	0	0
Settlements, Assets	(5)	(3)	(15)	(9)
Balance-End of Period, Assets	223	209	223	209
Net Realized Gains/Losses Attributable to Changes in Fair Value at the Balance Sheet Date, Assets	$ 0	$ 0	$ 0	$ 0