Investments (Short-Term and Long-Term Investments) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 18,844	$ 19,331
Securities, Available for sale Debt Securities, Gross Unrealized Gains	374	317
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(46)	(221)
Available-for-sale Securities, Debt Securities	19,172	19,427
Available-for-sale Equity Securities, Amortized Cost Basis	1,628	1,576
Securities, Available for sale Equity Securities, Gross Unrealized Gains	24	9
Securities, Available for sale Equity Securities, Gross Unrealized Losses	(16)	(13)
Available-for-sale Securities, Equity Securities	1,636	1,572
Held-to-maturity securities, Amortized Cost	517	543
Securities, Held to maturity, Unrecognized Holding Gain	3	1
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	520	544
Total investments, Amortized Cost	20,989	21,450
Total investments, Gross Unrealized Gains	401	327
Total investments, Gross Unrealized Losses	(62)	(234)
Investments, Fair Value Disclosure	21,328	21,543
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Securities, Debt Securities	19,172	19,427
U.S. Government and Agency Obligations [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,839	2,211
Securities, Available for sale Debt Securities, Gross Unrealized Gains	3	5
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(3)	(21)
Available-for-sale Securities, Debt Securities	1,839	2,195
Held-to-maturity securities, Amortized Cost	178	181
Securities, Held to maturity, Unrecognized Holding Gain	3	1
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	181	182
State and Municipal Obligations [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	6,609	6,902
Securities, Available for sale Debt Securities, Gross Unrealized Gains	221	147
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(4)	(72)
Available-for-sale Securities, Debt Securities	6,826	6,977
Held-to-maturity securities, Amortized Cost	28	28
Securities, Held to maturity, Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	28	28
Corporate Obligations [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	7,459	7,265
Securities, Available for sale Debt Securities, Gross Unrealized Gains	113	130
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(22)	(60)
Available-for-sale Securities, Debt Securities	7,550	7,335
Held-to-maturity securities, Amortized Cost	311	334
Securities, Held to maturity, Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Accumulated Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	311	334
U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,053	2,256
Securities, Available for sale Debt Securities, Gross Unrealized Gains	27	23
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(13)	(61)
Available-for-sale Securities, Debt Securities	2,067	2,218
Non-U.S. Agency Mortgage-Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	884	697
Securities, Available for sale Debt Securities, Gross Unrealized Gains	10	12
Available-for-sale Debt Securities, Accumulated Gross Unrealized Loss, before Tax	(4)	(7)
Available-for-sale Securities, Debt Securities	$ 890	$ 702