Debt - Narrative (Details) (USD $)	Dec. 31, 2013
Debt Disclosure [Abstract]
Face value of senior notes	$ 1,200,000,000
Commercial paper available for issuance under an uncommitted private placement program	500,000,000
Uncommitted short-term bank lines of credit under the Federal Reserve system	260,000,000
Uncommitted short-term bank lines of credit available through the secured Federal Reserve short-term discount window	70,000,000
Secured FHLB short-term borrowing capacity	15,500,000
Uncommitted short-term bank lines of credit	$ 14,100,000