Investments (Short-Term and Long-Term Investments) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Available-for-sale Securities, Debt Securities	$ 19,427
Available-for-sale Equity Securities, Amortized Cost Basis	1,576	668
Securities, Available for sale Equity Securities, Gross Unrealized Gains	9	10
Securities, Available for sale Equity Securities, Gross Unrealized Losses	(13)	(1)
Available-for-sale Securities, Equity Securities	1,572	677
Held-to-maturity securities, Amortized Cost	543	839
Securities, Held to maturity, Unrecognized Holding Gain	1	8
Securities, Held To Maturity, Unrecognized Holding Loss	0	0
Total debt securities - held-to-maturity, Fair Value	544	847
Total investments, Amortized Cost	21,450	19,926
Total investments, Gross Unrealized Gains	327	833
Total investments: Gross Unrealized Losses	(234)	(9)
Investments, Fair Value Disclosure	21,543	20,750
Debt Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	19,331	18,419
Securities, Available for sale Debt Securities, Gross Unrealized Gains	317	815
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(221)	(8)
Available-for-sale Securities, Debt Securities	19,427	19,226
U.S. Government and Agency Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	2,211	2,501
Securities, Available for sale Debt Securities, Gross Unrealized Gains	5	38
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(21)	(1)
Available-for-sale Securities, Debt Securities	2,195	2,538
Held-to-maturity securities, Amortized Cost	181	168
Securities, Held to maturity, Unrecognized Holding Gain	1	6
Securities, Held To Maturity, Unrecognized Holding Loss	0	0
Total debt securities - held-to-maturity, Fair Value	182	174
State and Municipal Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	6,902	6,282
Securities, Available for sale Debt Securities, Gross Unrealized Gains	147	388
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(72)	(3)
Available-for-sale Securities, Debt Securities	6,977	6,667
Held-to-maturity securities, Amortized Cost	28	30
Securities, Held to maturity, Unrecognized Holding Gain	0	0
Securities, Held To Maturity, Unrecognized Holding Loss	0	0
Total debt securities - held-to-maturity, Fair Value	28	30
Corporate Obligations [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	7,265	6,930
Securities, Available for sale Debt Securities, Gross Unrealized Gains	130	283
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(60)	(4)
Available-for-sale Securities, Debt Securities	7,335	7,209
Held-to-maturity securities, Amortized Cost	334	641
Securities, Held to maturity, Unrecognized Holding Gain	0	2
Securities, Held To Maturity, Unrecognized Holding Loss	0	0
Total debt securities - held-to-maturity, Fair Value	334	643
U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	2,256	2,168
Securities, Available for sale Debt Securities, Gross Unrealized Gains	23	70
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(61)	0
Available-for-sale Securities, Debt Securities	2,218	2,238
Non-U.S. Agency Mortgage-Backed Securities [Member]
Available-for-sale Debt Securities, Amortized Cost Basis	697	538
Securities, Available for sale Debt Securities, Gross Unrealized Gains	12	36
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(7)	0
Available-for-sale Securities, Debt Securities	$ 702	$ 574