Fair Value Measurements (Unrealized Losses And Fair Value Of Investments With Unrealized Losses) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015 investment
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	1,009
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	$ 2,584
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	1,018
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,604
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0
Asset-backed Securities
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	664
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	1,251
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	671
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	1,263
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0
Foreign Government Debt Securities
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	131
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	582
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	133
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	589
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0
US Government Agencies Debt Securities
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	92
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	259
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	92
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	259
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	0
Other Debt Obligations
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	122
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than Twelve Months, Fair Value	492
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	122
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	493
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 0