Accounting for Derivatives - Interest Rate Risk (Details) - Derivatives designated as hedging instruments: - Interest rate swaps $ in Millions	Mar. 31, 2016 USD ($)
Notional Disclosures
Notional amount of interest rate swaps	$ 500
Derivative expiring in 2018
Notional Disclosures
Notional amount of interest rate swaps	300
Derivative expiring in 2019
Notional Disclosures
Notional amount of interest rate swaps	100
Derivative expiring in 2020
Notional Disclosures
Notional amount of interest rate swaps	$ 100

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant