Fair Value Measurements and Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	Jun. 30, 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	33	42
Investment securities at a loss position for less than 12 months, aggregate unrealized holding losses	2	1
Investment securities at a loss position for less than 12 months, estimated fair value	95	88
Total notional amount of outstanding contracts in cash flow hedging relationships	18	$ 18
Maximum collateral required	$ 4