Fair Value and Investment Securities Maturity Distribution Based on Contractual Terms of Investment Securities (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014
Available-For-Sale Amortized Cost
Due within 1 year	$ 1,476
Due after 1 year through 5 years	1,025
Due after 5 years through 10 years	14
Due after 10 years	12
No contractual maturity	25
Total	2,552
Available-For-Sale Fair Value
Due within 1 year	1,476
Due after 1 year through 5 years	1,027
Due after 5 years through 10 years	14
Due after 10 years	11
No contractual maturity	26
Total	$ 2,554