Fair Value Measurements (Assets and Liabilities Measured At Fair Value On A Recurring Basis Using Unobservable Inputs (Level 3)) (Details) (USD $) In Millions, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2014	Dec. 31, 2013
Estimated Fair Value	$ 3,398	$ 2,713
Available-for-sale Securities [Member]
Available-for-sale Securities, Amortized Cost Basis	3,316	2,642
Available-for-sale Securities, Gross Unrealized Gain	6	1
Available-for-sale Securities, Gross Unrealized Loss	1	2
Estimated Fair Value	3,321	2,641
Available-for-sale Securities [Member] | Asset-backed Securities [Member]
Available-for-sale Securities, Amortized Cost Basis	1,611	1,177
Available-for-sale Securities, Gross Unrealized Gain	4	1
Available-for-sale Securities, Gross Unrealized Loss	1	1
Estimated Fair Value	1,614	1,177
Available-for-sale Securities [Member] | Foreign Government Debt Securities [Member]
Available-for-sale Securities, Amortized Cost Basis	826	846
Available-for-sale Securities, Gross Unrealized Gain	2
Available-for-sale Securities, Gross Unrealized Loss	0	1
Estimated Fair Value	828	845
Available-for-sale Securities [Member] | US Government Agencies Debt Securities [Member]
Available-for-sale Securities, Amortized Cost Basis	361	211
Available-for-sale Securities, Gross Unrealized Gain	0	0
Available-for-sale Securities, Gross Unrealized Loss	0
Estimated Fair Value	361	211
Available-for-sale Securities [Member] | US Treasury Securities [Member]
Available-for-sale Securities, Amortized Cost Basis	408	350
Available-for-sale Securities, Gross Unrealized Gain	0
Estimated Fair Value	408	350
Available-for-sale Securities [Member] | Certificates of Deposit [Member]
Available-for-sale Securities, Amortized Cost Basis	103	53
Available-for-sale Securities, Gross Unrealized Gain	0	0
Available-for-sale Securities, Gross Unrealized Loss		0
Estimated Fair Value	103	53
Available-for-sale Securities [Member] | Other Security Investments [Member]
Available-for-sale Securities, Amortized Cost Basis	7	5
Available-for-sale Securities, Gross Unrealized Gain	0
Available-for-sale Securities, Gross Unrealized Loss		0
Estimated Fair Value	7	5
Trading Securities [Member]
Estimated Fair Value	77	72
Available-for-sale Securities [Member]
Estimated Fair Value	3,321	2,641
Other Assets [Member]
Estimated Fair Value	$ 77	$ 72