Fair Value Measurements and Derivative Instruments (Narrative) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Fair Value Disclosures [Abstract]
Investment securities at a loss position for more than 12 months, aggregate unrealized holding losses	$ 1	$ 1
Investment securities at a loss position for more than 12 months, estimated fair value	35	42
Investment securities at a loss position for less than 12 months, aggregate unrealized holding losses	1	1
Investment securities at a loss position for less than 12 months, estimated fair value	76	88
Total notional amount of outstanding contracts in cash flow hedging relationships	17	18
Maximum collateral required	$ 3