Equity, Stock Repurchase Activities (Details) $ / shares in Units, shares in Millions					3 Months Ended			9 Months Ended
	Jul. 23, 2015 $ / shares	Apr. 23, 2015 $ / shares	Jan. 27, 2015 $ / shares	Jul. 23, 2014 USD ($) $ / shares shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) $ / shares shares	Mar. 31, 2014 USD ($) shares	Sep. 30, 2015 USD ($) $ / shares shares	Sep. 30, 2014 USD ($) agreement institution $ / shares	Jul. 31, 2015 USD ($)	Oct. 31, 2014 USD ($)	Feb. 28, 2014 USD ($)
Accelerated Share Repurchases [Line Items]
Cash dividends declared per common stock (in dollar per share) | $ / shares	$ 0.10	$ 0.1	$ 0.1		$ 0.10	$ 0.10		$ 0.3	$ 0.10
Common stock repurchased under stock repurchase program average purchase price (in dollars per share) | $ / shares					$ 28.01	$ 23.44		$ 24.78
Stock repurchase program, authorized amount												$ 2,100,000,000
Stock repurchased and retired | shares					1.8	23.5		42.4
Common stock repurchased and retired under stock repurchase program, value					$ 50,000,000	$ 550,000,000	$ 900,000,000	$ 1,100,000,000
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, remaining authorized repurchase amount					$ 625,000,000			$ 625,000,000
Stock repurchase program, authorized amount						$ 1,200,000,000			$ 1,200,000,000	$ 3,900,000,000		$ 1,200,000,000
Additional amount authorized under Stock Repurchase Plan										$ 500,000,000	$ 1,300,000,000
Stock repurchased and retired | shares							33.3
Accelerated share repurchases, remaining amount recorded in equity				$ 300,000,000