Equity, Stock Repurchase Activities (Details) $ / shares in Units, shares in Millions				3 Months Ended			6 Months Ended
	Apr. 23, 2015 $ / shares	Jan. 27, 2015 $ / shares	Jul. 23, 2014 USD ($) $ / shares shares	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2014 USD ($) $ / shares	Mar. 31, 2014 USD ($) shares	Jun. 30, 2015 USD ($) $ / shares shares	Jun. 30, 2014 USD ($) institution agreement $ / shares	Oct. 31, 2014 USD ($)	Feb. 28, 2014 USD ($)
Accelerated Share Repurchases [Line Items]
Cash dividends declared per common stock (in dollar per share) | $ / shares	$ 0.1	$ 0.1		$ 0.1	$ 0		$ 0.2	$ 0
Stock repurchase program, authorized amount									$ 3,400,000,000	$ 2,100,000,000
Stock repurchased and retired | shares				23.2			40.6
Common stock repurchased under stock repurchase program average purchase price (in dollars per share) | $ / shares				$ 25.83			$ 24.64
Common stock repurchased and retired under stock repurchase program, value				$ 600,000,000		$ 900,000,000	$ 1,000,000,000
Number of accelerated share repurchase agreements | agreement								2
Number of financial institutions for ASR | institution								2
Accelerated share repurchases, aggregate payments made during period						$ 1,200,000,000
Additional shares repurchased under ASR | shares			16.0
Total accelerated share repurchases, shares repurchased | shares			49.3
Accelerated share repurchases, weighted average repurchase price (in USD per share) | $ / shares			$ 24.35
2014 Stock Repurchase Program [Member]
Accelerated Share Repurchases [Line Items]
Stock repurchase program, authorized amount					$ 1,200,000,000			$ 1,200,000,000		$ 1,200,000,000
Additional amount authorized under Stock Repurchase Plan									$ 1,300,000,000
Stock repurchased and retired | shares						33.3
Accelerated share repurchases, remaining amount recorded in equity			$ 300,000,000
Stock repurchase program, remaining authorized repurchase amount				$ 175,000,000.0			$ 175,000,000.0