Fair Value Measurements and Derivative Instruments (Narrative) (Details) - USD ($) $ in Millions	Mar. 31, 2016	Dec. 31, 2015
Fair Value Disclosures [Abstract]
Investment securities at a loss position for more than 12 months, aggregate unrealized holding losses	$ 1	$ 2
Investment securities at a loss position for more than 12 months, estimated fair value	39	36
Investment securities at a loss position for less than 12 months, aggregate unrealized holding losses	1	2
Investment securities at a loss position for less than 12 months, estimated fair value	59	146
Total notional amount of outstanding contracts in cash flow hedging relationships	16	$ 13
Maximum collateral required	$ 5