Short-Term and Long-Term Debt (Schedule of Junior Subordinated Notes) (Details)	12 Months Ended
	Dec. 31, 2016 USD ($)
Junior Subordinated Institutional Notes June 2008
Debt Instrument [Line Items]
Principal Amount	$ 600,000,000
Interest Rate	8.88%
Interest Rate Subsequent to Optional Redemption Date	5.00%
Junior Subordinated Institutional Notes August 2012
Debt Instrument [Line Items]
Principal Amount	$ 1,000,000,000
Interest Rate	5.88%
Interest Rate Subsequent to Optional Redemption Date	4.18%
Junior Subordinated Institutional Notes November 2012
Debt Instrument [Line Items]
Principal Amount	$ 1,500,000,000
Interest Rate	5.63%
Interest Rate Subsequent to Optional Redemption Date	3.92%
Junior Subordinated Retail Notes December 2012
Debt Instrument [Line Items]
Principal Amount	$ 575,000,000
Interest Rate	5.75%
Junior Subordinated Retail Notes March 2013
Debt Instrument [Line Items]
Principal Amount	$ 710,000,000
Interest Rate	5.70%
Junior Subordinated Institutional Notes March 2013
Debt Instrument [Line Items]
Principal Amount	$ 500,000,000
Interest Rate	5.20%
Interest Rate Subsequent to Optional Redemption Date	3.04%
Junior Subordinated Institutional Notes May 2015
Debt Instrument [Line Items]
Principal Amount	$ 1,000,000,000
Interest Rate	5.38%
Interest Rate Subsequent to Optional Redemption Date	3.03%