Fair Value and Investment Securities Distribution of Financial Instruments, Measured at Fair Value on a Recurring Basis (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Fair Value, Option, Quantitative Disclosures
Amounts held in escrow for the preliminary U.S. merchant class litigation settlement	$ 540		$ 540
Fair Value, Measured on Recurring Basis	1,640		1,199
Fair Value, Inputs, Level 1
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	108	[1]	98	[1]
Fair Value, Inputs, Level 2
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	1,532		1,101
Fair Value, Inputs, Level 3
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	0		0
Municipal securities
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	120		135
Municipal securities | Fair Value, Inputs, Level 1
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	0	[1]	0	[1]
Municipal securities | Fair Value, Inputs, Level 2
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	120		135
Municipal securities | Fair Value, Inputs, Level 3
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	0		0
U.S. government and agency securities
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	215	[2]	199	[2]
U.S. government and agency securities | Fair Value, Inputs, Level 1
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	101	[1],[2]	85	[1],[2]
U.S. government and agency securities | Fair Value, Inputs, Level 2
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	114	[2]	114	[2]
U.S. government and agency securities | Fair Value, Inputs, Level 3
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	0	[2]	0	[2]
Corporate securities
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	1,031		618
Corporate securities | Fair Value, Inputs, Level 1
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	0	[1]	0	[1]
Corporate securities | Fair Value, Inputs, Level 2
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	1,031		618
Corporate securities | Fair Value, Inputs, Level 3
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	0		0
Asset-backed securities
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	168		178
Asset-backed securities | Fair Value, Inputs, Level 1
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	0	[1]	0	[1]
Asset-backed securities | Fair Value, Inputs, Level 2
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	168		178
Asset-backed securities | Fair Value, Inputs, Level 3
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	0		0
Other
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	106		69
Other | Fair Value, Inputs, Level 1
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	7	[1]	13	[1]
Other | Fair Value, Inputs, Level 2
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	99		56
Other | Fair Value, Inputs, Level 3
Fair Value, Option, Quantitative Disclosures
Fair Value, Measured on Recurring Basis	$ 0		$ 0

[1] During 2015, U.S. government securities were reclassified from Level 2 to Level 1 due to a reassessment of the availability of quoted prices. Prior period amounts have been revised to conform to the 2015 presentation.

[2] Excludes amounts held in escrow related to the U.S. merchant class litigation settlement of $540 million at March 31, 2015 and December 31, 2014, which would be included in Level 1 of the Valuation Hierarchy. See Note 6 (Accrued Expenses and Accrued Litigation) and Note 11 (Legal and Regulatory Proceedings) for further details.